Included are all declared wars and wars that were undeclared in which the United States lost at least 10,000 dead.
1775 - 1782 Revolutionary War.
1812 - 1815 War of 1812 (Note: The war actually began with the French invasion of Austria in 1805)
1848 Mexican-American war.
1861 - 1865 U.S. Civil War
1889 Spanish-American War.
1917-1918 World War I (War actually began in 1914)
1941-1945 World War II (War in Europe actually began in 1939, Asia began in 1937)
1950-1953 Korean War
1965 - 1973 Vietnam War
The greatest time period between wars is the current period between the end of the war in Vietnam to the present. I put this together to demonstrate how war is common even in democracies. War is a constant factor throughout written history. (I suspect unwritten history as well.) Warfare is human conflict at it’s most violent level. Warfare is part of human nature. We find many reasons to wage war. Defensive wars generally do not require any excuses. But what is defensive war? You may actually start the shooting while acting in a perceived defensive manner. Most people fight and risk their lives to protect their way of life. What is required is to present the war as defense of that way of life. In this case, many times even an otherwise peaceful population will agree to fight.