Israel-Palestine Conflict?

Here's a question I've been meaning to ask for a while now. In WWI, Great Britain conquered what is now Israel from the Ottoman Empire. In the Balfour Declaration, Great Britain decided to give part of the land to the Jews which is now Israel. So here's my question. If it was the British that conquered palestine in WWI, why are the palestinians angry at the Jews, shouldn't they be upset at Britain for having conquered it in the first place?