Do you mean on North American soil?
Well, then there were 5: The French and Indian, Revolution, War of 1812, Civil War, and WW2. (Pearl Harbor and the Japanese took one of the Aleutian Islands off the coast of Alaska.)
While certainly an important event in US history, the US Civil War didn't "lead" or "start" the study of US History.
The Us Civil War was the bloodiest war recorded in US history.
The statement that US history is not taught past the Vietnam War is not correct. US colleges and secondary schools have quite different US history boundaries. There is a mass of US history running past the War in Vietnam.
The Library of Congress in Washington DC has many thousands of government records. Without a doubt, the history of tariffs can be found there covering the US Civil War and most of US history.
Traditionally it has been the US Civil War and WW2.
The American Civil War
The Vietnam War is considered a loss, because the communists did conquer the country that the US fought to preserve from the communists. There are many others, but the only wars in US history that were declared are The American Revolution, The War of 1812, World War One, and World War Two. But if you count unofficial wars, then there are many where we did not fulfill our goal, Vietnam being the biggest one.
If you mean only involving the US, than the Civil War.
The French and Indian War was the longest US war before 1850.The longest US war in history was the Vietnam War.
just one? Civil War
The civil war is more US history because the whole country was at war. The northern states wanted slavery to end. The southern states wanted slavery to thrive.
The US has been fighting in Afghanistan longer it was fighting in Vietnam. It is the longest war in US history.