Sandi...The trigger comes first...and for many it's unknown. Most times once "established", especially for those where the tendency or inherited quality, the initial trigger/offender/etc is long gone and the immune system continues to automatically react against the body in a specific established pattern in speciically established areas.
I'll assume a stimulation in the body that causes the colon to react normally can cause it to overreact in a way toward a flare. Some people call the colon the second or little brain....so, it's definitely related/connected to much of the body's natural/immune processes anyway.
The body has a long memory, and trying to break the pattern or at least slow it down to not continually overreact would be a good way to deal.
If only many of us had the initial trigger dealt with...maybe the disease pattern wouldn't have been established. I had continual diarrhea foryears before I was sent to a GI who did the tests and diagnosis. Most of us wouldn't think that diarrhea would lead to UC anyway unless it's already known in a family and early signs are dealt with early.