Historians Jonathan Shneer and James Gelvin have acknowledged that the British leadership supported Zionism in order to persuade American Zionist leaders to push the U.S. into WW I. Here’s a quote from Gelvin’s The Israel-Palestine Conflict: One Hundred Years of War: “Two of Wilson's closest advisors, Louis Brandeis and Felix Frankfurter, were avid Zionists. How better to shore up an uncertain ally than by endorsing Zionist aims?”
Zionist leaders like Samuel Landman admitted their role in entangling the U.S. in war: the best and perhaps the only way (which proved so to be) to induce the American President to come into the War was to secure the co-operation of Zionist Jews by promising them Palestine, and thus enlist and mobilise the hitherto unsuspectedly powerful forces of Zionist Jews in America and elsewhere in favour of the Allies on a quid pro quo contract basis. Thus, as will be seen, the Zionists, having carried out their part, and greatly helped to bring America in, the Balfour Declaration of 1917 was but the public confirmation of the necessarily secret "gentleman's" agreement of 1916