1) Nope they had decided to go in and wipe the Jews out as soon as the 1947 partition plan was put in place. The Jews were fighting for survival from 1929 when the grand mufti spread his BLOOD LIBELS that resulted in the Hebron massacre.
Here it is from Wiki
1948 Arab?Israeli War - Wikipedia, the free encyclopedia
The General Assembly decision on Partition was greeted with overwhelming joy in Jewish communities and widespread outrage in the Arab world.
In Palestine, violence erupted almost immediately, feeding into a spiral of reprisals and counter-reprisals. The British refrained from intervening as tensions boiled over into a low-level conflict that quickly escalated into a full-scale civil-war.[19][20][21][22][23][24]
From January onwards, operations became increasingly militarized, with the intervention of a number of Arab Liberation Army regiments
inside Palestine, each active in a variety of distinct sectors around the different coastal towns. They consolidated their presence in Galilee and Samaria.[25] Abd al-Qadir al-Husayni came from Egypt with several hundred men of the Army of the Holy War. Having recruited a few thousand volunteers, al-Husayni organized the blockade of the 100,000 Jewish residents of Jerusalem
2) so the Jewish groups were only taking control of the crumbs the UN had thrown them while the arab states were actively warmongering. And the arab states were heard to state they would wipe out the Jews.
The Arab League gave reasons for its
invasion in Palestine in the cablegram:[59]
the Arab states find themselves compelled to intervene in order restore law and order and to check further bloodshed
the Mandate over Palestine has come to an end, leaving no legally constituted authority
the only solution of the Palestine problem is the establishment of a unitary Palestinian state.
Some unofficial statements before the war had been more aggressive. Secretary Azzam Pasha, according to an interview in an 11 October 1947 article of Akhbar al-Yom, said: "I personally wish that the Jews do not drive us to this war, as this will be a war of extermination and a momentous massacre which will be spoken of like the Mongolian massacres and the Crusades".
As for the west bank the Jews had already made agreements with Abdullah for him to annexe the west bank.
Same source
In 1946–47, Abdullah said that he had no intention to "resist or impede the partition of Palestine and creation of a Jewish state."[64] Ideally, Abdullah would have liked to annex all of Palestine, but he was prepared to compromise.[65][66] He supported the partition, intending that the West Bank area of the British Mandate allocated for the Arab state be annexed to Jordan.[67] Abdullah had secret meetings with the Jewish Agency (at which the future Israeli Prime Minister Golda Meir was among the delegates) that reached an agreement of Jewish non-interference with Jordanian annexation of the West Bank (although Abdullah failed in his goal of acquiring an outlet to the Mediterranean Sea through the Negev desert) and of Jordanian agreement not to attack the area of the Jewish state contained in the United Nations partition resolution (in which Jerusalem was given neither to the Arab nor the Jewish state, but was to be an internationally administered area). In order to keep their support to his plan of annexion of the Arab State, Abdullah promised to the British he would not attack the Jewish State.
