Why did the UN ign Jerusalem to be an international city n 1947?

i'm doing a presentation tomorrow on the whole palestinian - Israeli conflict and for my part of the presentation i have to talk about this. except there is soo much depth to the conflict that it was impossible to get all the details. did they do this to avoid more conflict? i have no idea lol and when obama says that "the 1967 border must be the basis for negotiations to set up a future palestinian state" what exactly does it mean? all i know is that he believes that "the dream of a jewish and democratic state cannot be fulfilled with permanent occupation"