Short answers, pulled from the story.
Mandatory Palestine was a British administrative territory in the region of Palestine that existed between 1920 and 1948. From 1922 it operated under a formal League of Nations mandate, classified as a Class A Mandate, the highest grade awarded to post-war territories based on their capacity for self-governance.
The Balfour Declaration, issued on the 2nd of November 1917, was a statement by the British government promising support for the establishment of a Jewish national home in Palestine, while stipulating that the civil and religious rights of existing non-Jewish communities must not be prejudiced. It was incorporated into the preamble of the mandate itself and became the central source of conflict between the Arab and Jewish populations throughout the mandate period.
Mohammad Amin al-Husseini was an Arab nationalist appointed by High Commissioner Herbert Samuel as Grand Mufti of Jerusalem in 1921, and elected President of the Supreme Muslim Council in 1922. He controlled substantial Waqf and orphan funds as well as the Islamic courts, and played a key role in organizing violent opposition to Zionism, including leading the Arab Higher Committee during the 1936-1939 Arab Revolt.
The Arab Revolt was an uprising that began in April 1936 with a general strike organized by the Arab Higher Committee and lasted until March 1939. By its end, more than 400 Jews and 200 British had been killed, and at least 10 percent of the adult Arab male population had been killed, wounded, imprisoned, or exiled. The revolt severely damaged Palestinian Arab political cohesion and military capability in the lead-up to the 1948 war.
The 1939 White Paper limited legal Jewish immigration to 15,000 per year; once that quota was exceeded, Jews fleeing Nazi persecution were interned or deported to places such as Mauritius. A clandestine effort called Aliya Bet organized by Mossad LeAliyah Bet brought tens of thousands more by sea, though the British Royal Navy intercepted many vessels and two ships were sunk by Soviet submarines. After the war, 250,000 Jewish refugees remained in displaced persons camps in Europe despite U.S. President Harry S. Truman's repeated requests that 100,000 be admitted immediately.
The mandate ended at midnight on the 14th of May 1948, after the British Parliament passed the Palestine Bill, which received Royal assent on the 29th of April 1948. On the afternoon of the 14th of May, David Ben-Gurion declared the State of Israel. The 1948 Arab-Israeli War that followed resulted in Israel encompassing about 78 percent of the former mandate territory, with Transjordan annexing the West Bank and Egypt seizing the Gaza Strip.