The American Revolution
From 1775 to 1782, the Americans faced off against the largest empire in the world. Led by General Washington they won.
Duration: 80 months Deaths: 4435 military (approximately 25,000 total)
The War of 1812
Some call it the Second War of Independence, for when it ended and the US had fought Great Britain to a stalemate, America's independence was assured.
Duration: 30 months Deaths: 2260 military (approximately 20,000 total)
A dispute over Texas joining the Union resulted in US conquest of California and the balance of the Southwest.
Duration: 20 months Deaths: 13,283
The Civil War
It was America's bloodiest war as brother fought brother.
Duration: 48 months Deaths: 191,963 military (approximately 625,000 total)
World War I
Millions died in the fields of Europe, sometimes while fighting over a few disputed yards.
Duration: 19 months Deaths: 116,516
World War II
It was a war like no other, and covered all corners of the globe.
Duration: 44 months Deaths: 405,399
The Korean War
Some call it the forgotten war, but for two years America fought a full fledged war to keep South Korea free.
Duration: 37 months Deaths: 62,321 (54,245 recovered/8075 no remains)
It was previously the longest war that the United States fought and the only one that the United States lost.
Duration: 90 months Deaths: 59,961 (58,220 recovered/1741 no remains)
The last war America took part in the 20th century took place when Kuwait was invaded by Iraq.
Duration: 1 month Deaths: 383
Global War on Terror (includes Operation Enduring Freedom & Iraqi Freedom)
Operation Enduring Freedom: War came to America on September 11th 2001 with an attack on NY and Washington. Not since the Battle of Antietam had so many Americans perished in a day.
Iraqi Freedom: On March 19th 2003 the United States invaded Iraq to overthrow the government of Saddam Hussein. To present, US troops continue to fight an insurgency there.
Duration: 104 months to date (Enduring)/86 months to date (Iraqi)
Deaths: 5015 (as of Feb 6, 2010)
Other "Minor" Conflicts (see full list here)
Sources: radicalrevolution.net, wikipedia, crs report for congress
Photos: American Battle Monuments Commission