If it would be easier to provide example(s) of the wars you would have supported, please do. The question is probing your anti-war motivation. Anti-war motivations are sometimes based on strict constitutional complaince to form, pacifism, ideological enmity, etc. In cases other than pacifism, sometimes I find it helps me to understand a person's opposition by asking the counter question of which wars meet approval and why.
I am in favor of any war which defends our country or the rights of it's citizens. I am opposed to any war which has any other purpose. And I am well aware that people in favor of nation building and adventurism will aways attempt to paint their favorite wars as doing those two things. Some are tricked, I am not.
Therefore, I support WWII and the War against Afghanistan. Off the top of my head I can't think of any others.