How does the nationalism that developed over the Berlin Wall in Germany differ from the situation in Northern Ireland with the Catholics and Protestants?

Answer 1

Many Germans on each side saw the Wall as an imposed dividing constraint. In NIreland, fanatics on both sides did not trust the other side, and in fact, wanted to supress them violently, if not control them.

Answer 2

There was never a wall between Northern Ireland and the Irish Republic. Germany was divided artificially by countries that conquered it in WW2. The division was based upon disagreements between the occupying powers, not religious differences of the Germans.