On what basis was Jordan's annexation of the West Bank and east Jerusalem illegal? On what basis was Israel's subsequent annexation legal?
Under the partition plan, Jerusalem was to have remained an independent entity under an international trusteeship. Its holy sites were to have been open to all pilgrims. Its Arab residents could have opted for citizenship in the Arab state and its Jewish residents could have opted for Israeli citizenship.
Transjordan seized the eastern half of Jerusalem in the 1948 war. In 1950, Jordan annexed that section of Jerusalem. It also barred Jewish people from worshipping at the Western Wall, Judaism's holiest site.
During the 1967 war, after Jordan attacked Israel in joining the war on the side of Egypt, Israel captured the eastern half of Jerusalem.
Legally, if the circumstances under whichTransjordan captured and annexed East Jerusalem, specifically a war in which Transjordan was the aggressor, established Jordan's legal claim, then Israel's legal claim was at least as valid as the precedent for capture and annexation was no different. In fact, Israel's legal claim would be stronger, as Israel was not the aggressor in the 1967 war. The Jewish people also have the longest-standing historic claim.
In any case, the final status of East Jerusalem will likely be established in negotiations. Jordan and Israel have already agreed upon how they will resolve the city's status.
I would prefer that the city remain undivided. It can be done without compromising Arab/Palestinian interests by permitting the Arabs/Palestinians joint sovereignty over predominantly Arab sections of East Jerusalem/Muslim holy sites, guaranteeing open access to all holy sites, and permitting the city's Arab residents to become citizens of either Jordan or a Palestinian state. My guess is that Israel will eventually cede portions of East Jerusalem, as that is what Israel agreed to do during the Oslo process. My concern is that the Palestinians will overreach with respect to Jerusalem--ignoring both Israeli and Jordanian interests in the process--and, as a result, make it more difficult to achieve a final settlement.