Shortly before the Axis invasion of Yugoslavia, certain high ranking army and airforce officers, backed by Great Britain, staged a coup against the Yugoslav monarchy on 27 March. 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 neither of the non-Serb national groups (Slovenes and Croats) were prepared to fight in defence of what they viewed as Serbian-dominated 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 10 April 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.