In 1850 there were 80 per cent Arabs in Palestine. The rest were 15 per cent Christians and 5 per cent Jews. The first Zionist settlement in Palestine was established in 1878. In 1896 the Austrian author Theodor Hertzl published "Der Judenstaat" that advocated a Jewish state in Palestine or elsewhere (South Africa or South America). So the idea of Israel is originally an "artificial" political (Zionist) idea. Over the next decades the Jewish immigration grew to such proportions that conflicts between the Arabs and Jews were unavoidable. By the end of WWII the Jews in Palestine had increased, mostly through immigration (official or illegal), to about 31 per cent with a landownership of 6 per cent. By this time three main Zionist terrororganizations had emerged: The Haganah, Irgon and Stern.
1945 to 1948 are extremely volatile years with several assassinations (lord Moyne, British Minister on Nov. 1944, Folke Bernadotte, UN peacebroker in 1948, both by Stern), terrorattacks (Deir Yassin massacre, bombing of the King David Hotel) and ethnic clensing operations (coastal villages i.e) performed by the the Haganah, Irgon and Stern. By 1948 the Zionists had organized a well equipped and highly trained army of about 90,000. In the early months of 1948 the Zionist organizations had performed eight major operations under the Haganah's Plan D ("Dalet"). These offensive operations took place on Arab land outside the territory alloted to the Israelis by the UN in November 1947. The Haganah attacked and captured i.e. the city of Jaffa which the UN had ruled belonged to the Arabs. By contrast the Arab forces were very much a third world army, ill-equipped and poorly trained.
After WWII the British had dropped the hot potato of Palestine in the lap of the UN who on November 29th, 1947 voted on an amended partition plan calling for a 56.5 % of Palestine for a Jewish state, 43 % for a Palestinian one and internationalization of Jerusalem. This despite the fact that the Jews only consisted of about 31 per cent of the population in Palestine and owned even less land (7 per cent).
On May 14th 1948 the state of Israel was declared in Tel Aviv. On the following day, May 15th, the British mandate over Palestine ended and the Israeli state declaration took effect.
The Israeli aggression forced the neighbouring Arab countries (Jordan, Syria and Egypt) to go into the areas allotted to the Palestinians where the Israelis were operating. However by the end of 1948 the Arabs had lost the war and the Dispossession began.
No land allotted to Israel by the UN had been attacked by Arab forces. All fighting had taken place on land alloted to the Palestinians by the UN. By the end of 1948 Israel had conquered 78 per cent of Palestine. Far more than what the UN had alloted. All maps were redrawn and given new Hebrew names. 750 000 Palestinians became refugees in their own homeland.
"Palestine was divided into three parts. The 1949 armistice agreements gave Israel control over 78 percent of the territory of British Mandate Palestine. Jordan occupied and annexed East Jerusalem and the hill country of central Palestine, thereafter known as the ?West Bank? of the Jordan River. Egypt took temporary control of the coastal plain around the city of Gaza, later referred to as the Gaza Strip. Both Jordan and Egypt held on to these respective territories until the 1967 war, during which Israel occupied the West Bank and Gaza. The Palestinian Arab state provided for in the United Nations partition plan was never established."
http://www.palestinecenter.org/palestine/1948war.html
http://www.palestine-net.com/history/bhist.html
http://www.pmwatch.org/pmw/snakebite/Wars.html