Watch the movie Michael Collins. There was once a good reason to fight.
But nations evolve. And that antipathy should have faded away. When you start targeting innocent people, there's a problem.
The strange thing is the Republic of Ireland doesn't want a united Ireland. It would change their whole political and economic system and it would probably lead to a civil war as bad as Yugoslavia.
But as Ireland was the only democracy to send commiserations to Germany on Hitler's death, who knows what they would do?
But nations evolve. And that antipathy should have faded away. When you start targeting innocent people, there's a problem.