This event was probably the most crucial in setting up the events prior to the war, since Germany was not okay with the heavily unbalanced and bias restrictions set in the Treaty.
Seeking to build Germany into the power it deserved, Hitler joined a small political party in the hopes that he could use them to reobtain it's former glory and national spirit.
Italy was the first nation to set up a fascist government, thanks to the nationalist goals of Benito Mussolini.
This was the start of a communist state in Russia, thus putting it at uneasy odds with the fascist nations that sprung up around this time.
Not only did this mark the beginning of Japan's campaign for land seizure, but it inspired those of other countries as well.
Nazism eventually caught on, to the point that the Nazis were given (or rather took) complete political control of Germany. Once this was achieved, several steps would be taken to secure the future of Germany and its empire.
This was the beginning of Nazi Germany's campaign for lebensraum, to spread their influence and empire beyond the constraints set on them by the League of Nations.
Uneasy about the war overseas, America was determined to remain a neutral force, thus establishing these acts. They would not fight or interfere in the war, but still shipped aid to the Allies.
In order to pacify their aggressive campaign, Britain attempted to stop their reach by giving them Sudetenland...to little avail.
Surprising the world and their neighbor by offering peace, Hitler decided to create a nonaggression pact between Nazi Germany and the Soviet Union in order to avoid a two-fronted war as in the previous one.
This was the farthest the Third Reich reached westward, and was most likely a purely "teach those who opposed me a lesson" move, since that seemed to be the primary motive of this occupation.
This Lend-Lease Act enabled the US to send aid overseas without actually getting involved in the war itself, saving it the losses.
The culmination of the Nazis' anti-Semitic campaign, the "final solution" to rid the world of the Jewish race was to burn every last one of them (an end goal that thankfully was never achieved).
The attacks on Pearl Harbor were the final push the US and their neutrality needed to finally enter the war.
Up until this point, white males were the sole occupants of the US military and workforce. However, after staunch declaration otherwise by African Americans and women, those who wanted to be allowed to fight for their country, spots were open and these groups sent production rates and role calls skyrocketing.
In order to stand their ground and create one of the most significant battle of the war, the Soviet Union basically destroyed the 6th Army division of the Nazi forces, ending their eastward campaign and effectively bringing the war into the landing strip.
Both battles were significant towards bringing the war to a close: D-Day was the day the US army struck the coast of Western Europe to liberate them of their Nazi occupations; the Battle of the Bulge was the battle in which the remaining Jews in Nazi concentration camps were liberated, as well as the Nazis' last offensive of the war.
On this day, the Nazis finally announced unconditional surrender to the Allies, thus ending the war after six long years.
Not only was this the final (albeit one-sided) confrontation between Japan and the US (to which the former surrendered near-instantly), but this was also the first (and last) instance where an atomic bomb was used on another country during war.
In order to both replace the League of Nations as a superior peacekeeping and international cooperation and development, a whopping 51 countries signed a declaration that created the United Nations.
With the war finally over, Nazi officials (or at least those still alive) were convicted and prosecuted for their crimes against humanity, and most of them were sentenced to death.