The Balfour Declaration was a November 2, 1917 letter from British Foreign Secretary Arthur James Balfour to Lord Rothschild that made public the British support of a Jewish homeland in Palestine. The Balfour Declaration led the League of Nations to entrust the United Kingdom with the Palestine Mandate in 1922
The Balfour Declaration was a product of years of careful negotiation. After centuries of living in a diaspora, the 1894 Dreyfus Affair in France shocked Jews into realizing they would not be safe from arbitrary antisemitism unless they had their own country.
In response, Jews created the new concept of political Zionism in which it was believed that through active political maneuvering, a Jewish homeland could be created. Zionism was becoming a popular concept by the time World War I began.
The Balfour Declaration was a product of years of careful negotiation. After centuries of living in a diaspora, the 1894 Dreyfus Affair in France shocked Jews into realizing they would not be safe from arbitrary antisemitism unless they had their own country.
In response, Jews created the new concept of political Zionism in which it was believed that through active political maneuvering, a Jewish homeland could be created. Zionism was becoming a popular concept by the time World War I began.

World War I and Chaim Weizmann
During World War I, Great Britain needed help. Since Germany (Britain's enemy during WWI) had cornered the production of acetone -- an important ingredient for arms production -- Great Britain may have lost the war if Chaim Weizmann had not invented a fermentation process that allowed the British to manufacture their own liquid acetone.
It was this fermentation process that brought Weizmann to the attention of David Lloyd George (minister of ammunitions) and Arthur James Balfour (previously the British prime minister but at this time the first lord of the admiralty). Chaim Weizmann was not just a scientist; he was also the leader of the Zionist movement.

Diplomacy
Weizmann's contact with Lloyd George and Balfour continued, even after Lloyd George became prime minister and Balfour was transferred to the Foreign Office in 1916. Additional Zionist leaders such as Nahum Sokolow also pressured Great Britain to support a Jewish homeland in Palestine.
Alhough Balfour, himself, was in favor of a Jewish state, Great Britain particularly favored the declaration as an act of policy. Britain wanted the United States to join World War I and the British hoped that by supporting a Jewish homeland in Palestine, world Jewry would be