Defensive: Revolutionary War
Defensive: War of 1812
Defensive: Mexican American War
Defensive: Civil War (the Union was defending it's existence, the South was the offending party)
Offensive: Spanish American War
Defensive: Gulf War I
Offensive: Clinton's War in Yugoslavia.
Yeppers, clearly all the wars the United States have fought are offensive, all righty, just look at that list. Two out of 13. That clinches it. Clearly US troops following lawful orders must bear the cost of their service because Comrade Osama orders it.