The "again" at the end of your comment makes me wonder to what extent you believe the US was involved with propping up the IRA. They smuggled guns from America but I haven't seen anything credible beyond that.
I'm really torn on the whole thing. I don't want there to be a barrier between the British and Irish, but I also see the appeal of Ireland being whole. We've come so far in my lifetime and I like we've ended up in this situation where the two countries are just open to each other. It's a really strong statement given where things were less than 50 years ago.
Remember that Ireland and Northern Ireland both make up the island of Ireland. The Irish live in (the republic of) Ireland and the Northern Irish live in the northern part of Ireland (Northern Ireland), which is part of the UK.