Without the Balfour Declaration there would probably one cannot be certain be no Israel. And without Israel, the post-1945 history of the Middle East would certainly be profoundly different.
Curiously, despite its importance, Arthur Balfour's Declaration, in November, 1917, throwing the full weight of the British Government behind the Zionist dream of creating a Jewish homeland in Palestine, is scarcely remembered by the ordinary Briton. For that reason, the "man on a Clapham omnibus" feels that the Arab-Israeli conflict is nothing to do with the British people, but he is wrong.
In historical terms, the Declaration is remarkable: when else has a government granted an international pressure group the right to set up a "homeland" on somebody else's land? And that land had not at that time even come into the hands of the nation making the gift.
It takes the arrogance of an Empire to dispose of property in such a way, but three years later the formula was written into the Sevres Peace Treaty between the Ottoman Empire, which had ruled Palestine until World War I, and the Western Allies. It later became enshrined in the conditions of the British Mandate for Palestine, by which the League of Nations granted Britain control of the territory.
The practical effect of British support for a Jewish homeland was mass immigration of Jews into Palestine, with the active encouragement of Zionist activists. From being a small minority of the population some 25,000 out of 400,000 in 1880, by one account the Jewish population increased to about 600,000 by 1945, out of a total of 1.8 million. At times, the British authorities tried to block Jewish immigration, but with limited success. It should be a matter for shame that the most stringent and successful efforts to turn away Jews were made at the height of the Nazi persecution.
In 1948, Britain, whose policy had been largely responsible for Arab-Jewish tensions in Palestine, walked away from its Mandate despite the lack of agreement between the two protagonists on the future of the territory. The Jews, who were well prepared, immediately seized control of their promised homeland, expelling large numbers of Palestinians in the process. And they turn that homeland into a Jewish State.
Since then, Israel and the rights of the Palestinians have been the central political issue of the Arab world and the rallying cry of the Muslim religious establishment. Energy that should have been used productively to develop the Arab world has been diverted into fighting Israel. Tyrants have rallied support by threatening to march on Israel (tyranny loves having somebody to hate) and religious madmen have inspired terrorist attacks against the West by linking Israel to the "Crusaders".
Without Balfour's assurances, it is likely that many of the Jews who sought refuge in Palestine would have joined others of their people who fled Europe to enrich American society by their presence. The ancient Jewish communities that flourished in many Arab cities might have remained, instead of being driven out on a tide of hatred sparked by the events of 1947.
There is no doubt that in such circumstances, US-Arab relations would have run along a much smoother path. American influence over the Arab oil industry would not have taken such a blow in 1973 and the "oil shock" would have been avoided. But as the American attitude towards Arab Gulf oil reserves was entirely exploitative, the longer US oil majors controlled the price of crude, the slower the development of the infrastructure of the Arab world would have been.
Other effects of the Balfour treaty are simply impossible to gauge. Would the Shah of Iran have survived if there had been less antipathy towards the West? Would the Palestinians have established a modern, Mediterranean democracy? not unlikely, as they were among the most sophisticated of the Arab people. Would the nationalism of Gamal Abdul Nasser have taken root, without a symbol to hate in the shape of Israel? Would the Ba'athism of Assad and Saddam ever have come into being? And would there be an Al Qaeda?
We have no way of knowing the answers to these questions, we cannot step through a glowing portal into a parallel universe like characters in a sci-fi movie; all we can say is that the influence of the Balfour Declaration on events in the Middle East has been both enormous and incalculable. For good or ill, the fate of millions of people was sealed by these words:
"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".
Of course, the Jews took a State, not a homeland, and the civil rights of the non-Jewish communities in Palestine have been deeply prejudiced. But it was Balfour's Declaration that provided the impetus the Zionist idea needed, regardless of whether they adhered to its sentiments.