Beyond the problems of inadequate equipment and incomplete mobilization, the Royal Yugoslav Army suffered badly from the Serbo-Croat schism in Yugoslav politics. "Yugoslav" resistance to the invasion collapsed overnight. The main reason was that none of the subordinate national groups; Slovenes, Croats were prepared to fight in defence of a Serbian Yugoslavia. The only effective opposition to the invasion was from wholly Serbian units within the borders of Serbia itself. In its worst expression, Yugoslavia's defenses were badly compromised on April 10, 1941, when some of the units in the Croatian-manned 4th and 7th Armies mutinied, and a newly-formed Croatian government hailed the entry of the Germans into Zagreb the same day.