The British motivation was relatively straightforward. It was the execution that got screwed up. The British Government, finding itself at war with the Ottoman Empire in 1914 and being second only to that Empire in influence in the region, had to give consideration to what was to be done with Ottoman possessions in the Middle East once the war was over.
Herbert Samuel (later Viscount Samuel) was Posmater-General at the time and a member of the War Cabinet (the first practising Jew to hold a Cabinet post in the UK). He circulated a memo urging the government to promise to create a Jewish homeland in Palestine. The then Prime Minister, Asquith, was in favour of reforming the Ottoman Empire, so the memo got spiked. Then Asquith resigned and was replaced by David Lloyd George, who favoured dismantling the Ottoman Empire,so the memo got some interest as a potential solution for post-War stabilisation of the region.
But by 1917, the situation had changed. The Western Front was in deadlock. Russia was having a revolution and the US had yet to fully engage. Britain needed men and money. For money they turned, as they had done during the Peninsular War a century before, to the powerful, wealthy and Jewish House of Rothschild. For men, they had a large pool of Russian refugees from the Revolution, many of whom were young Jewish men. The idea wasto offer these young men (technically deserters from the Russian military) the option of conscription into the British Army, or being shipped back to Russia. In order to encourage the first option, the Foreign Secretary, Arthur Balfour gave a letter to Lord Rothschild to pass on to the Zionisr Federation of great Britain and Ireland. This is what is known as the Balfour Declaration. I give the text in full:
His Majesty's Government view with favour the establishment in Palestine of a national home for the Jewish people, and will use their best endeavours to facilitate the achievement of this object, it being clearly understood that nothing shall be done which may prejudice the civil and religious rights of existing non-Jewish communities in Palestine, or the rights and political status enjoyed by Jews in any other country.
All very nice-sounding. However, they had forgotten, or not taken into account, the role of the Arabs in the War. The Ottomans held a lot of Arab territory and the Arabs didn't like it. Early in the War, they started to rebel against the Ottomans and quickly ran into trouble. The British, from their base in Egypt, began to supply the Arabs with materials and advisors - the best known of them being T E Lawrence ('Lawrence of Arabia') - all of which quickly turned the tide in favour of the Arabs.
Lawrence and his colleagues believed that the Ottoman Empire was to be broken up and the lands returned to the Arabs. It seems unlikely that Lawrence, in particular, would have known about the Declaration, as his integrity was absolute, and he would surely have told his Arab friends had he known.
Whether this was a case of deliberate hiding, or simply a failure of comunication, I am unwilling t guess. There was a lot going on in a lot of places and this wouldn't have been the only cock-up.
What is clear is that the Zionists took the Declaration and subsequent League of Nations and United Nations Resolutions as carte-blanche to do as they pleased in Palestine.
But Britain, caught between a rock and a hard place and scrabbling for help, could hardly have foreseen the consequences. Such a thing would not have happened in normal times.
Would you believe I used to be a lecturer?