Kurt Vonnegut swore to the widow of his best war-time buddy that his Dresden novel (Slaughterhouse-Five) would be an anti-war book before she welcomed him into her home.
Vonnegut enlisted into the U.S. Army in early 1943, at the height of our involvement in World War II. Whether he enlisted rather than waiting to be drafted is not clear. As a 4th generation German American (he makes this absolutely clear on the title page of Slaughterhouse-Five), he may very well have been conflicted fighting Germany. Whether he could have opted for the Asian theater of war is also not clear.
He published his anti-war novel, Slaughterhouse-Five, in 1969, 24 years after the central event (the Allied fire-bombing of Dresden) of the book. It is not unusual for writers to take years (or decades) before they can write about traumatic events in their own lives (and to fictionalize it, too).
But what IS unclear above all else is: the reader is left not really understanding what the phrase “anti-war” means to the guy writing an anti-war novel.
Surely, you are kidding; it is self-evident what “anti-war” means. For example, the United States of America is an anti-war nation, our people are “anti-war,” Americans hate war.