I promise that this is purely out of curiosity and not a question born of a homework assignment.
I'm currently taking a course on the history of the Middle-East, and in learning about the history of modern Iraq we were told that Abdullah I was in line for the first kingship of Iraq but was instead moved to the kingship of Transjordan by the English and French to make way for Faisal I to rule Iraq.
I asked our professor why this was the case instead of simply installing Faisal I in Transjordan, but he didn't have an answer for me. I'm hoping this subreddit does. Thank you.
Faisal wanted, had the support, and initially ruled Syria. As the day-to-day commander of the Arab revolt and with the broadest popular support, rule of the largest Arab population center in the former Ottoman territories was a natural place for him to land. Unfortunately the French had prior claims to that territory, and as a result they ousted Faisal after about five months.
Britain was placed in an awkward position of having to rectify all of it's wartime aims and promises towards the Arabs and towards the Hashemites in particular. With Syria out of the question, and Palestine reserved to the British in order to project the national Jewish homeland in Palestine that was described int he Balfour Declaration, that pretty much left Transjordan and Iraq.
Between these two, Transjordan was the less desirable of the two. There wasn't really much there, Amman was a small village in 1920.
Management of Iraq was, itself, problematic. The British, in emulation of Indian policy, first went towards incorporating Iraq directly into the empire, but this ended with the Iraqi revolt of 1920 which saw a change in the local British administrator as well as overall policy.
Instead the British settled on the "Sharifian Solution." Wherein they would try to settle their debt to the Hashemites and the rulership of the Middle East in one go. Rather than the creation of one united Arab kingdom in the territories described in the Hussein-McMahon correspondence, Faisal would get Iraq, and, in theory, Abdullah would get Transjordan.
This was concluded at the Cairo Conference in 1921.
Now while Faisal's apportionment seems basically fair, Abdullah's reward, particularly for an elder son, seems quite sparse. This is explained by the implication given by the British that they had no objections to Faisal eventually ruling over Palestine or even Syria. So while Transjordan seemed initially seemed like a rather small apportionment it had great promise. This was, of course, never to be, and in fact Abdullah's relationship with his Syrian officers, who had their eyes on retaking Damascus, became a more direct point of contention not just with the British but with Abdullah's own Jordanian subjects who resented his lack of attention on domestic affairs.
Eventually he was disuaded from pursuing Syria, but never really gave up hope for ruling Palestine, or at least the West Bankers. He would eventually be assassinated in East Jerusalem after the Arab failure in the 1948 War against the creation of Israel.
Source wise:
Two books I always reccomend on this subject as being quite good, Rogan's "The Arabs: A History" and Fieldhouse "Western Imperialism in the Middle East", for Faisal in Iraq see Charles Tripp's history of that country. On Abdullah and Jordan see Mary Wilson's "King Abdullah, Britain and the Making of Modern Jordan."