*Limited to one battle per war, with an unfortunate but inevitable western bias.
Part of the Greco-Persian Wars
Greece (Athens, Plataea) vs Persian Empire
Decisive Greek victory
The first Greek victory in the Persian invasion of Greece, this battle showed that the Persians weren't, in fact, invincible, a major psychological victory for the Athenians. The victory showed the young Athenian democracy that their system could survive, and marked the start of the Greek Golden Age. If the Persians hadn't been turned back, Athens would have been destroyed before it could basically invent western culture, and all of European history (and subsequently world history) would have been unrecognizable.
Part of the Second Punic War
Carthaginian Republic vs Roman Republic
Carthaginian tactical victory
Rome, determined to defeat Hannibal (the Carthaginian general) who had invaded Rome from the north by crossing the Alps, sent a massive army to meet him at Cannae. In what has been called one of the greatest tactical feats in military history, Hannibal's much smaller army annihilated the Roman army. Although Carthage went on to lose the war, because it was such a devastating defeat, it had significant effects on Rome. Rome reformed the structure of its army (introducing the cohort system they used to conqueror the known world) and gave singular command to Scipio Africanus, illegal under the Roman constitution, which foreshadowed the decline of the Roman political institutions. If Rome would have won the battle, they may not have learned their lesson in the Punic Wars, and have had a harder time conquering their neighbors later on.
Part of The Final War of the Roman Republic
Octavian vs Mark Antony and Ptolemaic Egypt
Decisive Octavian victory
This was a confrontation between rivals Octavian and Mark Antony, who both vied for power in Rome after Julius Caesar's supposed assassination (we know that he really lived, and today teaches at Granite Hills). Octavian's victory left him with complete control of the Mediterranean, and he changed his name to Augustus Caesar, becoming the first emperor of Rome. As well as marking the end of the Republic and the start of the Empire, the battle marked the end of the Hellenistic period, as Rome gained full control over Mark Antony's ally, Egypt. If Mark Antony would have won, he may have preserved the Republic, or may have become emperor himself, but with more eastern interests.
Part of the Roman-Germanic wars
Germanic tribes vs Roman Empire
Decisive Germanic victory
As the Roman commander Varus was marching his army to put down an uprising in Germania, his adviser Arminius slipped away to command a Germanic army that waited to ambush the Roman army. Varus walked right into the trap, and his army was completely destroyed. This was the last time Rome tried to conquer Germanic territory east of the Rhine, which has obvious consequences for the development of the region. If Rome had won, they would have had control over Germania, and it would have been integrated into the Empire and Romanized like other provinces, leading to a completely different history of the region.
Part of the Gothic War
Eastern Roman Empire vs Goths
Decisive Gothic victory
Although it was the Eastern Roman Empire that lost to the rebelling Goths at Adrianople, it would survive for another millennium, and they battle really marked the beginning of the end for the western half. The Roman army was destroyed, and it showed that the barbarians had become a powerful adversary. If the Romans had won, the barbarian invasion of Rome may have been postponed, but its collapse was imminent.
Part of the Islamic invasion of Gaul
Merovingian Franks vs Umayyad Caliphate
Decisive Frankish victory
In this battle, the Franks turned back the advancing Muslim armies, who had been conquering the know world for a century. After conquering Iberia, they made it into modern day France, where they were defeated. This battle preserved Christianity as the religion of Europe and stopped the expansion of Islam, as well as set up the Frankish dominance in western Europe that would shape European history. Had the Muslims won, the Umayyad caliphate would have expanded into Europe, along with Islam, completely altering world history from that point onward.
Part of the Hungarian invasions of Europe
East Francia and Bohemia (Germans) vs Magyars (Hungarians)
Decisive German victory
In the first national German battle against a foreign enemy, the Germans' defeat of the invading Hungarians ended a century of Hungarian pillaging in western Europe. It showed that the era of knightly cavalry had arrived, to replace the light nomadic cavalry of the Hungarians. It also convinced the Hungarians to settle down, creating the basis for the state of Hungary. If the Hungarians had won, they would have continued pillaging western Europe, altering it geography, and the state of Hungary would either not exist or be more westward.
Part of the Norman conquest of England
Normans vs English
Decisive Norman victory
After a succession struggle following the death of childless King Edward the Confessor, Harold was crowned king, but invaders from Normandy in France led by William II tried to challenge that. At Hasting, Harold was killed, and soon William became king. The Norman takeover of England completely reshaped English culture and society, that the English would impose on much of the world during imperialism. If the English had won, the history of Britain and the lands they came into contact with would be drastically changed.
Part of the Hundred Years' War
Kingdom of England vs Kingdom of France
Decisive English victory
At Crécy, the French tried to halt the English invasion, but failed do to new tactics used by the English. Even though the English went on to lose the war, the battle is significant due to the English use of dismounted knights and longbowmen, an evolution in Medieval warfare that would change the way battles were fought in Europe. If the French had won, it would have shown the superiority of the traditional method of fighting with mounted knights, and the evolution of warfare would have been postponed.
Part of the Polish–Lithuanian–Teutonic War
Kingdom of Poland and Grand Duchy of Lithuania vs Teutonic Order
Decisive Polish–Lithuanian victory
The Poles and Lithuanians crushed the crusading Teutonic Order, preserving Poland and Lithuania as independent nations. The victory was often later used in German propaganda, depicting the Teutonic Knights as noble civilization bringers, while the Russians showed them as bloodthirsty invaders. If the Teutonic Order had won, their order would have been preserved and remained the power in the region, and Poland and Lithuania may have ceased to exist, completely changing the map of northeastern Europe.
Part of The Byzantine–Ottoman Wars
Byzantine Empire vs Ottoman Empire
Decisive Ottoman victory
The Ottoman capture of Constaniople marks the final destruction of the Roman Empire in the form of the Byzantine Empire. The fall of Byzantium led to the rise of Russia as the "Third Rome," as well as giving the Europeans a new enemy in the south. This new enemy blocked trade though the Middle East, and so Euopeans began looking for new trade routes by sea, leading to the Age of Exploration. When the city fell, many Byzantine scholars fled to Italy, bringing with them the studies of ancient Greece and Rome, sparking the Renaissance. If the Byzantines had won, the Russian-Ottoman rivalry may never had developed, and the Renaissance and Age of Exploration may never have occured, completly changing modern history.
Part of the Granada War
Union of the Crown of Castile and Crown of Aragon (Spain) vs Emirate of Granada
Decisive Spanish victory
This was the final battle in the Spanish Reconquista, and Spain was unified under Christian hands. It led Spain to view itself as the guardian of Catholicism, which lead to further exploration and conquering. Jews and Muslims were forced to convert or be expelled. If Granada had won, Spain would have been set back in its attempts at Iberian unity, and its New World explorations (and discovery) may have been postponed.
Part of the Anglo-Spanish War
Kingdom of England vs Spanish Empire
Decisive Spanish defeat
This was the famous defeat of the "invincible" Spanish Armada by the English fleet. It marked the shift of naval power from the Spanish to the English, foreshadowing the shift in Empires. The battle protected England from Spanish invasion, and marked the transition from the use of ramming and boarding to the use of gunnery in naval combat. If the Spanish had won, they would have been able to invade England, and the Spanish dominance of the seas would have been perpetuated.
Part of the Thirty Years' War
Sweden (Protestants) vs Holy Roman Empire (Catholics)
Swedish Pyrrhic victory
Although Sweden tactically won the battle, they lost their king and leader of the Protestants in the Thirty Years' War, Gustavus Adolphus. This was the greatest consequence of the battle, and the Protestant campaign lost direction. Because of this, the Protestants weren't able to capture all of Germany, and the war became a stalemate until both sides agreed on peace. If the Catholics had won the war, they would have had an advantage in Germany, and may have been able to win the war outright.
Part of the Ottoman–Hapsburg wars
Holy League vs Ottoman Empire
Decisive Holy League victory
The Holy League was an alliance of Central European nations opposing the Ottoman invasion of Europe. By failing to take Vienna, the Ottomans were halted, and their expansion into Europe was ended. If the Ottomans had won, they would have continued to advance into Euorpe, altering the development of wherever they conquered.
Part of the War of the Spanish Succession
Grand Alliance vs France and Bavaria
Decisive Grand Alliance victory
The Grand Alliance was an alliance of most of the nations of western Europe united in opposing France's attempt at unification with Spain, which currently had no successor to the thrown. The Grand Alliance supported a Hapsburg successor, and in an attempt to knock out the Holy Roman Empire, France attempted to capture the Hapsburg capital, Vienna. They were intercepted by the Grand Alliance at Blenheim, and defeated. If the French had won the battle, they would have been able to knock the Holy Roman Empire out of the war, and possibly win, being able to unite with Spain, becoming the most powerful nation in Europe, by far. This would have given France a much greater role in European and world history.
Part of the Great Northern War
Sweden vs Russia
Decisive Russian victory
This battle marked the decline of Sweden and the rise of Russia as the power in northeastern Europe. The Swedish army was destroyed, and Russia won the Great Northern War, establishing itself as a power in Europe. If Sweden had won the battle, Russia would not have become a European power, significantly altering all subsequent world history.
Part of the French Revolutionary Wars
Kingdom of the French vs Prussia
Decisive French victory
After the French Revolution, many monarchies in Europe declared war on France fearing revolution in their own countries. Valmy was France's first major victory in these wars, and as such it was a major psychological victory that emboldened the National Convention to end the monarchy. Victory gave the Convention the morale that permitted the development of the French Revolution. If the French had lost, the Revolution may have been crushed or just slowed, and the radical phase may not have developed, significantly altering history.
Part of the Napoleonic Wars
France vs the Seventh Coalition
Decisive Coalition victory
After having been defeated and exiled, Napoleon returned to try to build an empire again, but was stopped at Waterloo by the Seventh Coalition, an alliance of nations opposing Napoleon. His defeat ended his reign as emperor a second (and final) time, and the wars Europe had constantly been in since the French Revolution. Waterloo marked the start of half a century of peace in Europe. If the French had won at Waterloo, Napoleon may have been able to keep conquering for a while longer, and then be defeated, or peace may have been made.
Part of World War I
France and United Kingdom (Allies) vs German Empire
Decisive Allied victory
The defeat of the Germans at the Marne marked the end of the German advance into France. After the Marne, the Western Front turned into a stalemate of trench warfare, ending the German hope of quickly knocking out France, and forcing them to fight a two front war, which ultimatly caused them to lose. If the Germans had won, they would have been able to knock France out of the war, and been able to focus on the Eastern Front, possibly leading to victory in the war, greatly changing world history.
Egyptian Empire vs Canaanites
In the first battle to have been recorded in what is accepted as relatively reliable detail, the Egyptians defeated Canaanite rebels in the Levant, asserting their dominance there. It expanded the Egyptian Empire to its greatest extent and ushered in the greatest time of prosperity for the empire. If the Canaanites had won, who knows what could have happened?
Part of the Wars of Alexander the Great
Hellenic League (Macedonians) vs Achaemenid Empire (Persians)
Decisive Macedonian victory
In one of the greatest victories in the conquests of Alexander the Great, the Macedonians (lead by Alexander) defeated a Persian army nearly twice their size. After the defeat, the Persian emperor Darius attempted to flee eastward, but was murdered, thus ending the Persian Empire. If the Persians had won, their empire would have been preserved, and influenced events in the region, and the havoc caused by Alexander the Great's conquests wouldn't have happened further eastward.
Part of Arab–Byzantine Wars
Byzantine Empire vs Rashidun Caliphate
Decisive Rashidun victory
Newly unified by Islam, the Arabs exploded out of Arabia to the north, coming into conflict with the Byzantine Empire, who were crushed by a smaller Arab force in one of the most decisive battles in all of history. If the Byzantines had won, Muslim expansion, central to world history for the next thousand years, would have been halted at the very beginning, making all subsequent world history unrecognizable.
Part of the Byzantine-Seljuk wars
Byzantine Empire vs Great Seljuk Empire
Decisive Seljuk victory
Keeping with the pattern (the Byzantines don't win a single battle on this timeline), the Byzantines are defeated by a much smaller force, leading to the Turkification of Anatolia. The loss started civil unrest throughout the empire, and marks the beginning of the long Byzantine decline. If the Byzantines had won, they would have been able to hold on to Anatolia for much longer, likely postponing its eventual fall five centuries later.
Part of the First Crusade
Crusaders vs Fatimid Caliphate
Decisive Crusader victory
Seeking to open the city to Christian pilgrims, the Crusaders successfully besieged Jerusalem. Upon entering the city, they massacred many Muslims and Jews. The Kingdom of Jerusalem was established, and would survive for another 200 years. If the Muslims had won, there likely would have been more crusades to try to take the city, and the increased European exposure to knowledge and products from the East would have been lessened.
Part of the Russo-Japanese War
Empire of Japan vs Russian Empire
Decisive Japanese victory
This was the deciding battle of the Russo-Japanese war, in which the Japanese were expected to be crushed by Russia. However, the Japanese won decisively, sinking almost the entire Russian fleet. This was the only decisive sea battle ever fought by modern steel battleships and the first naval battle in which radio played an important role. Russia's unexpected loss was a severe blow to the Romanovs, and it emboldened the Central Powers to go to war in 1914, believing Russia to be weak. If the Russians had won, they would have taken over Manchuria and Korea, and Japan would have been weakened, greatly effecting the outcomes of both world wars.
Part of World War II
Nazi Germany vs Soviet Union
Decisive Soviet victory
The Nazis were rapidly advancing into the Soviet Union, but stopped to capture Stalingrad. The Soviets held out, however, and the German force was destroyed. This marked the turning point of the war in Europe, as the Soviets started advancing westward, and the Nazis had to draw vast amounts of troops from the west to reinforce the east. If the Nazis had won the battle, they may have been able to advance all the way to Moscow, knocking the Soviets out of the war, drastically altering the course of World War II.
Part of the Chinese Civil War
Republic of China vs Communist Party
Decisive Communist victory
In the decisive battle of the Chinese Civil War, most of Chiang Kai-shek's (the leader of the Republic of China) troops were destroyed, and rivals soon forced him to resign. The Communists gained full control of the north and center of China, and when the United States stopped providing aid to the ROC, they quickly fell. If the Republic of China had won, the Communists would have been greatly weakened, and China may never have become communist.
Part of the First Indochina War
French Union vs Viet Minh
Decisive Viet Minh victory
The battle started as a French attempt to crush the Viet Minh rebels who were fighting for independence from French imperialism, but the Viet Minh took the advantage and destroyed the French force. This directly led to the French withdrawing from Indochina, diving the country at the 17th parallel, leading to the Vietnam war. If the French had won, the resistance would have been destroyed, they would have been able to hold onto their colony for a longer time, and the Vietnam War wouldn't have happened.
Part of the Vietnam War
Anti-Communist forces vs Viet Cong and North Vietnam
Anti-communist forces tactical victory
The Tet Offensive was a surprise attack launched by communist forces across Vietnam, and although the anti-communist forces (United States, South Vietnam, etc.) won, it had a large effect on the American government and public. The American public was appalled at the high American death counts, and people began to lose faith in the government and the war, which ultimately led to U.S. withdraw. If the Communists had won, the American withdraw would have likely happened sooner.
Part of the Spanish conquest of the Aztec Empire
Spain vs Aztec Empire
Decisive Spanish victory
The Siege of Tenochtitlan was the final battle in Cortés's conquest of the Aztec Empire. Once inside the city, they slaughtered everyone they could find and raped the women. Had the Aztecs won the battle, this would have set back the fall of their civilization, but probably not for long.
Spanish conquest of the Inca Empire
Spanish Empire vs Inca Empire
Decisive Spanish victory
In this battle the Inca leader Atahualpa was ambushed and captured, the first step in the Spanish conquest of the Inca Empire. Atahualpa was soon killed, and the Inca were left without a leader, making them easier to conquer. If the Inca had won, the Spanish attempt at conquering the Inca would have been severely set back, and conquest may have been postponed for quite some time.
Part of the Seven Years' War
Great Britain vs France
Decisive British victory
While only fought by a small number of troops, this battle, the culmination of a siege of Quebec City, turned out to be the deciding moment of the Seven Years' War. The French force was defeated, and the British now controlled Quebec; the French soon surrendered. The battle and subsequent British victory in the war led to Britain gaining the French colonies in North America and to the formation of Canada. If the French had won, Quebec would have remained under French control, and maybe there would be an independent Quebec today, and no Canada.
Part of the American Revolutionary War
United States vs Great Britain
Decisive American victory
In the decisive battle of the American Revolutionary War, American forces managed to surround the British army. The British fought two small battles to try to break out, but ultimately surrendered the entire army. The battle won the American the French support that was necessary for winning the war, and was overall the turning point in the war. If the Americans had lost, the Revolution would have not gotten French support, and likely would have failed; the American colonies wouldn't become independent and the American Revolution wouldn't have inspired revolutions around the world, drastically altering modern history.
Part of the American Civil War
United States vs Confederate States
The turning point in the American Civil War, this battle saw the turning back of the confederate invasion of the North. Never again did the Confederates make their own offensives. If the Confederates had won the battle, they would have been able to penetrate far into the North, possibly leading to a peace settlement and independent Confederacy, drastically altering American history as well as the history of all the places the Americans affected.