How did England obtain the right to deal Palestine?

This agreement resulted in the US entering WW1. WW1 without the US was at a stalemate and lots of people were dying. The people who wanted to take over Palestine offered getting the US into the war in exchange for the Balfour Agreement. Then the people who controlled US media did a 180. They had been keeping the US out of the war. Suddenly, the propaganda shifted to convince gullible Americans to join the fight.