I got trouble with my stomach while I was visiting India. Had the typical tourist diarrhea the entire stay, and got some antibiotics while I was there. Had no severe health trouble as far as I knew before I went on this vacation. This could be the kick in. If I got som bacterias while I was there, those could possible make the immunesystem react and maybe react in the wrong way, I use to say that my immunesystem have lost it's memory of how to do a proper job.
I don't think the Crohns started because I was in a foreign country, but because my immunesystem had lost it's ability to recognize the bacteria that entered the intestines. A memory loss of the immunesystem And in addition to that, maybe the system was weak because of stress and other factors.
All the best from