In issuing the Balfour Declaration in 1917, considered as the beginning of Israel’s legitimation by other nations, Britain could not have acted alone because it belonged to a wartime alliance. The Allied powers, especially Britain and France, but also Russia, Italy, and later America, were fighting together. Their policies had to be coordinated. It would have been unthinkable for Britain to have issued a public pledge regarding the future of territory yet to be taken in war without the prior assent of its wartime allies.
In expressing a broad consensus of the Allies, it might be seen as roughly comparable to a UN Security Council resolution today.
(The writer teaches Middle Eastern history at Shalem College in Jerusalem and is a visiting fellow at the Washington Institute for Near East Policy)