The Jews had occupied Palestine during Biblical times.
Under the rule of Ancient Rome, Jewish revolts were violently supressed - Jews expelled in 70 CE.
In the centuries following, Palestine became Arab, Muslim land + part of the Ottoman empire.
After WW1: Collapse of the Ottoman empire.
Britain then controlled Palestine by League of Nations mandate.
Jewish immigration to Palestine increased in 1920s and 30s, tensions with Arab population.
The Holocaust led to calls for Jews to have their own homeland.
1945 pressure increased on the British to take 100,000 Jewish settlers into Palestine, British refused.
Terrorist campaign into Palestine, hundreds of deaths - Britain couldn't sustain colonies and oversea territories and their economy was weakened by war - couldn't solve issue in Palestine and asked UN to intervene.
