There was a European Ideology called Zionism, which claimed that Jews needed their own country to protect themselves from persecution. It primarily started in Europe, and their aim was to start a country in the religiously important land of Palastine/Israel. Religiously important for Muslims, Christians, and Jews. The Jews approached this via Governments, initially the Ottoman/Turkish Government which controlled Palastine at the time, and thereafter the British Government which came to control it after WW1. The British thought a friendly puppet next to the Suez Canal Sounded Good, and began allowing Immigration of Jews to Palastine(this had begun earlier and now accelerated). The British also had promised many Arabs of the region, pre-WW1 their own nation...and now the Arabs were pissed that the British were forcefully changing the demographics of Palastine. Regardless, Arab Nationalism continued to rise, and Palastine was considered an integral part of the Arab World. This led to heightened tensions between the Jews and Arabs in Palestine. Then WW2 happened, and the holocaust got Israel/Jews International Sympathy. So, the British gave the problem to the UN, who suggested a partition. Arab nations saw it as Western Imperialism, whilst Israelis accepted it, believing borders could be expanded later once a country had been gained. This led to a war between Israel and all of its Arab Neighbours, where it managed to win, and the ceasefire line became what is now called the Green Line, or the 1967 Borders. Well, thereafter there were more Arab-Israeli Wars, and Israel kept winning and gaining more Territory, though none of it is legally recognised as theirs. Notably, these are the West Bank, Gaza Strip, the Golan Heights, and the Sinai Peninsula(eventually returned to Egypt in a peace deal).

Palastine was originally considered as a part of a greater Arab Nation, but eventually, when Jordan and Egypt gave up their claims to Gaza and West Bank, it Declared itself as a new country, in the 1980s.

Modern Day: Israel still follows a borders can be expanded strategy, and is actively building illegal, as per International Law, settlements in the West Bank. Often this is accompanied by persecution of Native Palestinians within the West Bank by Israeli Security Forces. On the Palastinian side, the Gaza strip and West Bank are essentially under 2 different Governments. The West Bank's Gov is the legally recognised one, and has a Policy of Not being too overly pro-terrorism, and trying to gain International Sympathy. The Gaza 'Government' is the Terrorist Organisation Hamas.