The Israelis were given the land when it was under control of the British, although all sides might not have found the situation favorable, the Israelis did NOT "steal" the land. It WAS given to them. Then they were attacked by the Arabs, and they WON the fight. They are under NO obligation to give anything to anyone.
The Arab-Israeli War of 1948
The Arab-Israeli War of 1948 broke out when five Arab nations invaded territory in the former Palestinian mandate immediately following the announcement of the independence of the state of Israel on May 14, 1948. In 1947, and again on May 14, 1948, the United States had offered de facto recognition of the Israeli Provisional Government, but during the war, the United States maintained an arms embargo against all belligerents.
Raising the Flag signified the Conclusion of the Conflict
On November 29, 1947, the United Nations General Assembly adopted Resolution 181 (also known as the
Partition Resolution) that would divide Great Britain’s former Palestinian mandate into Jewish and Arab states in May 1948. Under the resolution, the area of religious significance surrounding Jerusalem would remain under international control administered by the United Nations. The Palestinian Arabs refused to recognize this arrangement, which they regarded as favorable to the Jews and unfair to the Arab population that would remain in Jewish territory under the partition. The United States sought a middle way by supporting the United Nations resolution, but also encouraging negotiations between Arabs and Jews in the Middle East.
The United Nations resolution sparked conflict between Jewish and Arab groups within Palestine. Fighting began with attacks by irregular bands of Palestinian Arabs attached to local units of the Arab Liberation Army composed of volunteers from Palestine and neighboring Arab countries. These groups launched their attacks against Jewish cities, settlements, and armed forces. The Jewish forces were composed of the Haganah, the underground militia of the Jewish community in Palestine, and two small irregular groups, the Irgun, and LEHI. The goal of the Arabs was initially to block the Partition Resolution and to prevent the establishment of the Jewish state. The Jews, on the other hand, hoped to gain control over the territory allotted to them under the Partition Plan.
After Israel declared its independence on May 14, 1948, the fighting intensified with other Arab forces joining the Palestinian Arabs in attacking territory in the former Palestinian mandate. On the eve of May 14, the Arabs launched an air attack on Tel Aviv, which the Israelis resisted. This action was followed by the invasion of the former Palestinian mandate by Arab armies from Lebanon, Syria, Iraq, and Egypt. Saudi Arabia sent a formation that fought under the Egyptian command. British trained forces from Transjordan eventually intervened in the conflict, but only in areas that had been designated as part of the Arab state under the United Nations Partition Plan and the corpus separatum of Jerusalem. After tense early fighting, Israeli forces, now under joint command, were able to gain the offensive.
See more . . .
The Arab-Israeli War of 1948 - 1945 1952 - Milestones - Office of the Historian