First off, just a quick reminder of #forum-rules, the insults aren’t necessary in this discussion.
That aside, and more salient to the topic at hand, it sounds like there may have actually been something odd happening if the participation checkbox wasn’t available.
Normally you can opt in/out any time before matchmaking starts, regardless of whether the old War is still shown. You can even opt in/out for future Wars after matchmaking starts, just not the War that your alliance has already been matched for, of course.
@LucasDaoc did you not have the Participate in Wars checkbox option available at any point since the previous War, or did you just not check it at any point?