Clarify the question please. Does this ask which of our wars I would not have supported in advance?
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.
It is clear at this point that we will probably never see eye to eye on this issue in the foreseeable future. Only finding banned weapons will bring us together - you to our position - because regardless of any discovery, this war, IMO, was completely justified.