And...in the modern era, looking at who initiated wars (since, say, 1900 - 2010):
Republican initiated wars (Gulf War, War on Terror)
4,976 (as of August, 2010)
Democrat initiated wars (WW I, WW II, Korea, Vietnam)
636,438
Let's reiterate once more:
Democrats 636,438 Americans killed
Republicans 4,976 Americans killed
No contest
How convenient. Leave out the civil war, 625,000. Two percent of the population at the time.