SadCat, I wouldn't have been quite as aggressive in stating it as Bleda did, but he's correct. Google Janet Nelson, Susan Reynolds, and "feudalism."

NEVERTHELESS, you also have a very good idea. In Hungary (my research specialty), the Hungarian King in "early" and "high" exercises a level of authority that would make the throne of the Isle de France cry. Kingly authority is ABSOLUTE unless the throne is disputed. However, in case of succession issues or a King who's pushed his luck too far, the nobles WOULD refuse to bring their troops, as in at Mohi when the Hungarians fought the First Mongol Invasion, and many of the nobles wouldn't show up in time(pity for Europe, as we now know, with the publication of the Secret History, that the battle was much closer than we previously thought). Bela's authority was simply overwhelmingly shaky. Post-invasion, he can snap his fingers and generate armies so large that Jan Dlugosz writes that nobody dares to move when he's in the field.