Weir p. 17 See Note 69 p. 123 f.

William Yale wrote on this in The Near East: A Modern History (Ann Arbor: University of Michigan Press, 1968), 266-270.
book selection from internet archive

Yale, a descendant of the founder of Yale University, was an authority on the Middle East who had worked for the State Department in a number of roles in the Middle East, including as a member of the King Crane Commission, and worked for many years as a professor of history.

“Guide to the William Yale Papers, 1916-1972,” University of New Hampshire Library, accessed on January 1, 2014, Weir's referenced link is no longer active http://www.library.unh.edu/special/index.php/william-yale
Only descriptions are now found online. https://library.unh.edu/find/archives/collections/william-yale-papers-1916-1972
https://ead-pdfs.library.yale.edu/4060.pdf

Weir: Yale writes: “…the Zionists in England set about winning British support for Zionism. This the English Zionists successfully did by the end of 1916. It was an amazing achievement which required great skill, unfaltering energy, and determination. The methods by which the conquest of the British government was made were diverse and of necessity in some cases devious.”

He writes, “The Zionists in England well understood that British leaders would have to be approached on the basis of their interests and ideas,” and notes, “The means used were adapted admirably to the personal outlook and characteristics of the men to be influenced.”

Some were “persuaded that Zionism was a fulfillment of Old and New Testament prophesies.” Zionists also appealed to “the idealisms of many [British],” convincing them that this was a solution to anti-Semitism and could be an “atonement by Christian Europe for its long persecution of the Jews.”

Some top officials had to be persuaded “that Zionism was a noble and righteous cause of significance to the welfare of the world as well as to that of the Jewish people.”

Others were to be convinced that “by backing Zionism world-wide enthusiastic Jewish support for the allied cause could be assured.” Yale notes that in 1916 “the Allied cause was far from bright” and quotes a Zionist leader’s statements that Zionists worked to persuade British officials that “the best and perhaps the only way (which proved to be so) to induce the American President to come into the war was to secure the cooperation of Zionist Jews by promising them Palestine, and thus enlist and mobilize the hitherto unsuspectedly powerful forces of Zionist Jews in America and elsewhere in favor 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 ‘gentlemen’s’ agreement of 1916…”

Yale states that once “inner circles of the British government had been captured by the Zionists,” they turned their efforts to obtain French, Italian, and American acquiescence to the Zionist program.

For a detailed discussion of the Lusitania incident and other aspects of the U.S. entry into WWI see John Cornelius, “The Hidden History of the Balfour Declaration,” Washington Report on Middle East Affairs, November 2005, 44-50. Print. Online at
https://www.wrmea.org/2005-november/special-report-the-hidden-history-of-the-balfour-declaration.html