There was never a state called Palestine.
It is the name of a region given to it by the Romans, to remove the previous Jewish name for the area. There was never a significant Arab presence in the region. In the 1870s not more than a few thousand Arabs.
After the Ottoman empire was defeated WW1, it was decided to create a Jewish state within the region. The Arabs agreed.
77% of the region that was called Palestine was give to the Arabs for creation of Arab states. The dividing line was pretty much the Jordan river. The map clearly indicates how the region was divided in 1922.
Any creation of a new Palestinian state within Jewish land would be the creation of yet another Arab state. The land for Arab states had already been agreed upon in 1922.
The Arabs never accepted a Jewish state in practice. Arab radicals began terrorism and disturbances as early as the 1930s.
The only point to even argue seems to be that the League of Nations had no right to decide what to do with the region called Palestine. Yet it was the western powers than won WW1. Previous war victors had always decided what to do with the spoils of war. It was only the intervention of US President Woodrow Wilson that kept this area from being taken over by the victors this time, as he believe the era of colonialism and the practice of to the victor belongs the spoils was over.