This is a surprisingly hard question to answer. Part of the problem is deciding what we mean by "died in war." We could just count all the soldiers who died, or we could also include all of the civilians who were also killed by soldiers. Wars generally cause lots of disease and starvation, too. Farmland, water supplies, and homes are often destroyed (accidentally or on purpose) so many people have to go hungry and live in unsanitary conditions. These deaths due to disease and starvation are usually much higher than the number of people who died on the battlefield. Another problem is that it's not clear what we would call "American" wars. The USA took a major part in World Wars I and II, but the number of deaths caused or suffered by the Americans was really only a small fraction of the total.

To give you an example, in World War II, about 300,000 Americans died on the battlefield, about 15 million soldiers worldwide died on the battlefield, but about 58 million people died in total, including soldiers and civilians. I think the majority of those 58 million were people in China, Russia, and Eastern Europe, where Americans didn't really do much fighting. Of course these are all just estimates, since it's really hard to keep track of these things, especially the non-military deaths.

OK, all that aside, I'll try to answer your question. The total number of American soldiers who have died on the battlefield in wars is somewhere around 660,000 (most of these deaths came during WWII, WWI, and the Civil War). The total number of people who have died in these wars (including disease, etc.) breaks down something like this:

American Revolution: 52,000? (Only a rough estimate)
War of 1812: 30,000? (No good numbers)
Civil War: 600,000
Spanish-American War: 10,000? (Nobody really knows)
WWI: 16 million
WWII: 58 million
Korea: 2.7 million
Vietnam: 4.7 million
First Gulf War: 20,000 - 200,000 (there is still some dispute about the number of Iraqis who died)
Current Iraq war: 50,000 (some estimates range up to 650,000 - this is very controversial right now)

So the total is something like 82 million. Most of these were people not on the battlefield.

I hope this comes close to answering your question. I found a lot of these numbers on Wikipedia.org, which is a good place to do more research if you're interested.

In all the American wars there have been 651,008 Battle Deaths; and about 1.2million deaths during service in war time.About 42 million people have served in the military during wartime. About 1/50th of the people serving during a time of war have died. This is according to the Veterans Administration current as of 2002, so the most recent war is not included.

This is a very difficult question to answer. First of all, not all conflicts our country has are considered wars. For instance, the Korean War and Vietnam War (despite their names) never had congress declare open war in the regions. Also, statistics are conflicting between different sources. To make it even more complicated, do you mean the number of Americans that have died, or the number of people that have died, or the number of combatants that have died, etc? Certainly, too many people have died in wars already, and no matter how you slice it, this number is not small. Even just counting American combatant casualties in only declared wars would number well over a million. If you want to count all conflicts America was involved in (in our short 200 years of existence), and count noncombatant casualties, this number is at least as high as hundreds of millions (deaths including non-combatants and deaths by non-Americans as well as deaths caused by other countries).