"why would he joined up in an irish reg "

I wonder about this... like there's all of us who have citizenship and heritage in Canada, States, New Zealand, Australia, etc. but whose ancestors emigrated from the Isle of Man.

Now one of my Manx 2nd great grandfathers actually came from Ireland, so I wonder if he had the same fondness for Ireland that we have for the Isle of Man? Might his descendents have joined the British Army in Ireland rather than England because of that heritage?