America's transition from an agricultural economy to an industrial one. This impacted our country by changing how our economy functioned, the role our government played in our economy, and led to the large-scale manufacturing and distribution and retail we see today.
The Suffrage Movement was the movement for Woman's Rights. This impact our country by giving woman equal rights under the law to men, giving them the right to vote, and the rights to the Bill of Rights.
The Civil War was the war between the Union and the Confederation of the United States. This impacted our country in good and bad ways, leading to mass rail-lines that improve shipment, the release of all African-American slaves, and much more.
Prohibition was the national illegalization of alcohol. This event impacted our history by leading to the forming of mass organized crime and new methods for illegal substance trafficking.
The period after the large Wall Street Crash that led to poverty, unemployment, and other economic depressions in America. This impacted our country by destroying the lives of thousands, changing the way financial institutions are regulated, and led to several economic-support programs such as JobCorps, Food Stamps, and TANF.
World War 2 was a large war between the Allies and the Axis Powers, where America's involvement helped lead to the defeat of 3 large communist super powers (Italy, Germany and Japan). This impacted our country by largely scaling up our military, leading to our continued efforts in wars in foreign countries (War on Communism, War on Terror, etc.), changing the way food was produced, the way war was fought, and much more.
Tension between the Soviet Union and the US that led to a WMD arms race, the Cuban Missile Crisis, and more. This impacted our country by building our stockpile of nuclear weapons, the creation of the Hydrogen bomb, and our re-assertment of being a world super power when the Soviet Union collapsed.
War between North and South Korea, during which the US aided South Korea. This impacted our country by leading to another boost in our military size, American's level of involvement in foreign affairs, and the way we fought war.
War between North and South Vietnam, America supported South Vietnam as an anti-communist movement. This impacted our country by leading to the end of military drafting (mostly) and kick-started a large peace-movement.
The movement for African American rights and the end of segregation. This affected our country by giving African American's equal rights, truly equal rights, and thus many others including Mexican-Americans.