1910's - Woodrow Wilson was very pro-war despite campaigning for no war

1930's and 40's - Communists were anti-war until Russia got invaded and then were pro-war, like the rest of the left

1950's - The left was pro-war and Truman lost to Eisenhower who wanted to end the Korean War

1960's - The left was pro-war until they actually had to go fight and only the radical left was anti-war for a short time toward the end

1990's - Everyone was pro-war, including the left

2000's - They were pro Afghanistan, and only anti-Iraq after a year or so.

Historically, the right has been more isolationist. It's only with the advent of the neocons in the 70's that they've become very pro-war. 1971 really was a watershed year because the US had to start defending the dollar hegemony through military means.