The ethno-religious conflict in Northern Ireland dates back to the seventeenth century and the question of Irish sovereignty dates all the way back to the twelfth century!
It does seem like a lot of people have given up on the first two, but if it's not one of those then it's the third one. So we have to work towards making it one of the first two.
Apartheid started in 1948. It was around for quite a long time. And the roots of the division in Northern Ireland went back centuries. But yes, long running divisions are harder to solve. Harder != impossible. And look at history - stuff changes.