So a magic wand was not waved over Bosnia with reform happening quickly by saying 'No More Serfs', and Yugoslavia did their own share of kicking the can down the road, as the Austrian shared control with the Ottoman Empire from 1878 til 1908, as shown in the bit from the Wall of Text above
Yes, their kicking of the can, as it were, was still far more rapid than anything the Habsburgs did. The fact that a law was passed as early as 1921 to abolish serfdom says something, given that significant reforms to agricultural relations were not enacted by the monarchy until the twentieth century (and these fell well short of abolition). It was obviously far too delicate a situation to be resolved immediately by just outright abolishing serfdom - particularly as the nature of the landowner/serf relationships made it an ethnic and confessional issue, as well as an economic one. Yes, the problem was obviously far from being resolved in the early '20s - the underdeveloped situation of many Yugoslav lands ensured that this would be the case, regardless of what Belgrade did. But it was a step in the right direction. Also, B-H was under very little real Ottoman influence from 1878-1908 - while nominally still Constantinople's province, local administration (and thus control over land relations) was completely under the Habsburgs.
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and the A-H officials found the existing system was working, so left it mostly alone
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Lol. Yes, they found the existing Ottoman system 'working' in favour of their interests - which were, namely, to restore order in B-H following the Herzegovina Uprising, and to cultivate the favour of the local ruling classes, which was critical if they were to smooth the transition of the two provinces to Austro-Hungarian rule as peacefully as possible. For all this, they needed the loyalty of the Muslim beys and
agas to as great an extent as possible, and thus, large-scale agricultural reform was generally eschewed. There were greater allowances made to the serfs at the beginning of the twentieth century, allowing some to buy their freedom and acquire land - but this did little in the way of resolving the wider issue. By 1910, a full 68% of the Orthodox rural population (which was over 90% of their total population) was under some form of feudal obligations - a greater portion than either their Catholic or Muslim counterparts. See: Milan Gaković, "Rješavanje agrarnog pitanja," 14-15, (1970). I would also question the notion that the system was working all the way until WWI - there were famously widespread agrarian revolts in the north-western Krajina region in 1910, which had to be suppressed with military force. This was before Serb nationalism had truly penetrated rural society (which happened mainly during the Balkan Wars), and so it was mainly the result of economic disillusionment.