The Balfour declaration was an offer to sell Palestine to the Zionist movement in return for war loans and to bring America into WW1 on the side of the allies.
This is according to the Rothchild archives below.
Origins in The First World War
Beginning in 1916, the British hoped that in exchange for their support of Zionism, “the Jews” would help to finance the growing expenses of the First World War, which was becoming increasingly burdensome. More importantly, policy-makers in the Foreign Office believed that Jews could be prevailed upon to persuade the United States to join the War. At this time, there were very strong pro-Zionist feelings by many of the political elite and establishment. Many of Britain’s leaders, including Prime Minister David Lloyd George, and Balfour himself, felt for the Jews and their history. These men were deeply religious Christian Zionists. They had grown up on the Bible; the Holy Land was their spiritual home. They believed that modern Zionism would fulfil a divine promise, and re-settle the Jews in the land of their ancient fathers