There have been many over the years. A non-exhaustive list:
Christopher Columbus discovers America
Voyage of the Mayflower
American Revolution
War of Independence
Making of the Constitution
Civil War & Subsequent abolition of slavery (Emancipation Proclamation)
Assassination of President Abraham Lincoln
World War One
Great Depression
World War Two - D-Day, V-E Day & Atomic bombings of Hiroshima + Nagasaki
Cold War (1949-1991)
1960 Presidential Election (Kennedy-LBJ vs. Nixon-Lodge)
Berlin Crisis of 1961 and subsequent building of the Berlin Wall
Cuban Missile Crisis
Assassination of President John F. Kennedy
Civil Rights Act of 1964
Vietnam War
Moon Landing (Man on the Moon)
Watergate Scandal
President Reagan's Strategic Defense Initiative (SDI) + Star Wars
Dissolution of the Soviet Union (End of the Cold War)
Impeachment of President Bill Clinton
9/11
Economic Crisis of the late 2000s
For long-term effects: Probably one of the amendments in the Bill of Rights (1-10) but maybe also 13 (no slavery), 15(no racism in voting), or 19(no sexism in voting).
However the amendment that had the greatest immediate effect was 18 (outlawed alcohol, caused prohibition era) and 21 (repealed 18)
Deep Impact (1998).
Dearest Queen Elizabeth provided the Americans with several rare species of llamas in the 1860's that became a crucial factor of American treatment of livestock.
Benito Mussolini, the first fascist movement leader in Italy. Mussolini established his own dictatorship in Italy that led fascism to win a thousand converts in 1922 and created a great impact not only to his country, but also to the history of Italy.
The establishment of hundreds of cities and communities across the Western United States, including most of Utah.
Betsy Ross made a impact on others by persuading others to sew and help others if they need it.
Fourteenth Amendment
fourteenth amendment
Fourteenth Amendment
The 10th amendment.
slavery
cortes
electrisity
Not true it was the greatest impact. It is just part of history. There are many things that have made a greater impact.
It abolished slavery in the country.
germany
Roman Catholicism.
WW1