Yes, Palestine Was Southern Syria

Another confirming document, from 1919:

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And don't forget this: 

Arab demonstration, Jerusalem, 1919/1920. The banner on the left reads "We resist Jewish immigration", the banner on the right reads "Palestine is part of Syria". (Emphasis added) In the post-WWI Peace Settlement the League of Nations divided Syria and Palestine into French and British mandates. The Balfour Declaration of 1917, which pledged Britain's support for a Jewish National Home in Palestine, was included in the British mandate for Palestine.

The picture reflects the political tensions in Palestine after the British captured the area from the Ottoman Empire.  The region was being divided up by the Great Powers with France taking over Syria and Lebanon, and Great Britain assuming the mandate of Palestine (both sides of the Jordan River) and Iraq.  And in accordance with the 1917 Balfour Declaration, Palestine was to house the national Jewish home.  By 1922, the British had lopped off the eastern bank of the Jordan (some 70 percent of Palestine) to establish the Kingdom of Transjordan for Emir Abdullah.

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