Some say it goes back to 1917, and the Balfour Declaration. The Holocaust added to the lesser discussed killings by Stalin, guilted the Allies into living up to the "promise of a homeland." It is hard for me to begrudge Israel keeping the land it took after the entire Arab World (backed ny the Soviet Union) attacked them in the Yom Kippur War, added to what they controlled after the Six Day War, a few years earlier.
Modern China, which was established in the same era as Israel was, has boldly pursued a goal of uniting the empire that existed centuries ago, the same type of policy Israel is condemned for. During the years the Israelis were fighting the Arabs, China was taking over contested ethnic areas, without any protest of note. It could be said that China's treatment of Muslims under its control is far worse than what Israel has done. Yet all we hear is a slight peep, even from the Muslim countries. It would be easy to conclude that Israel has been singled out for special attention, by this comparison with China.