After the Ottoman empire fell the League of Nations passed the Palestine Mandate or British Mandate for Palestine. The British divided up the land into self-ruling Transjordan (what is now Saudi Arabia) and Palestine under British rule. When antisemitism in Europe started to increase in the 1920's Jewish people started to immigrate to the Palestinian region. People who were in Palestine did not like this massive immigration because they thought they were losing their Arab identity so after a number of conflicts the British first proposed a two state solution in 1937 with the Peel Commission.
After WWII the UN decided to partition the area in to an Arab State, a Jewish State, and an international zone. The Arabs did not like this because a majority of people living in the Jewish state were Arab, but they went along with the plan and Israel got recognition from the UN. After this declaration some Arab states (Jordan, Syria, Egypt, and Iraq) went to war with Israel and when Israel won they expanded their border beyond the previous agreement and divided most of the rest up between Jordan, Syria and Egypt.
I'm sure that isn't a complete history, but I hope I was able to get the basics down alright.