Why did the pan-Arabist Ba'ath party split into rival regional branches?

by AngelusNovus420

The Ba'ath party was created in 1947 in Syria. Its platform was pan-Arab social, economic, cultural and political unity — and it soon established regional wings in other Arab countries such as Iraq and Yemen. The party was popular enough to see members elected to the Syrian parliament, which played a role in the formation of the UAR, a 1958 political union of Egypt and Syria. The UAR lasted no more than a few years, and it all went downhill from there. Less than two decades after its foundation, the Ba'ath party had split into bitterly-opposed Syrian and Iraqi rival branches. Why and how did a successful party whose claimed raison d'être was pan-Arab unity so quickly ended up compromising the very unity it sought to uphold?

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Not sure if relevant, but /u/boldFrontier explains some of the things going on behind the scenes, which lead to their regional rivalry: https://www.reddit.com/r/AskHistorians/comments/uahgn9/why_have_syria_and_iraqs_ruling_baath_parties/