We could have avoided getting involved in WWI and Vietnam.
WWII was necessary, we had no choice due to the mistakes we made in WWII.
We had to go in Afghanistan after 9/11. In retrospect, we should have gotten out sooner. OBL dead. Time to say adios. That was in 2011. We should have given our troops 6 months to prepare for the withdrawal and get out by 2012.
WWI.