It seems simple, but it is hard to achieve.
We all know of the Religious killing each other over Israel and Jerusalem in particular. The Israelis have their state, the Palestinians want to have their own state. Lines have been drawn in the sand, nations of the world are backing either the Israelis or the Palestinians. Fighting for Jerusalem has caused the city to be split into sections.
However, it seems that the answer is quite clear.
Why doesn't the UN simply make Jerusalem an international city? It would be free from being torn apart by the 'warring factions' and it would be under the influence of the UN, so no one can get angry over one side or the other having it.