Yugoslavia was attacked by Nazi-Germany on April 6, 1941. The king and the government left the country by air on April 15 for exile. The Royal Yugoslav Army capitulated to the Axis Forces on April 17, just eleven days later from the outbreak of war. The Germans immediately dismembered the conquered country. The Kingdom of Yugoslavia was not only militarily defeated in war but also deprived of the right to exist as a state.
Before the Second World War the Yugoslav Army had a great prestige in Europe based on its contribution to the victory of the Allied Forces in the First Word War. Though encircled Yugoslavia's ultimate defeat was admittedly inevitable, it was nevertheless a great surprise that its Army presented only feeble performance and defeated within so short a time. Therefore immediately after the occupation of Yugoslavia the concerned parties began inquiring the reason and responsibility for such a disgraceful collapse of the Army and the Kingdom.
During the World War Serbian nationalist claimed that the treacherous behavior of Croats and other non-Serbian people of Yugoslavia was the main reason for a quick breakup of the Kingdom in April war of 1941. Though Communist party of Yugoslavia sharply objected to such claims, the decline and end of Communist control made it possible for these ideas to gain foothold in modern Serbian history. Naturally these theories were met by backlash of Croatian historians.
Considering such controversy, this article pointed out three reasons. The first factor was Yugoslav military unpreparedness. Surely the Yugoslav high command must have expected German armed intervention as an aftermath of the anti-Tripartite Pact coup on March 27 1941. However, when the German forces struck, the mobilization and concentration of Yugoslav defense forces had hardly begun. In the end, Yugoslavia was less than half mobilized.
The second factor was deficiency of defense plans. Before the war the Yugoslav General Staff worked out three defense plans one. However, all of these plans committed to a cordon type defense. Instead of massing their forces around strategic points, the Yugoslav command chose to scatter its forces and spread them along the entire perimeter of the country's frontier. It was easy for the German highly mechanized attack forces to break through the poor Yugoslav defense lines.
The third factor was the lack of fighting sprits among major elements of the Yugoslav Army. Shortly after the Germans attacked, entire Croat units simply threw away and quit fighting. There can be little doubt years of antagonism between the Serbs and Croats had a great influence over their morale. However, the persistence was missing among Serb elements of the Army. Good evidence is as follows. The German troops which started from Bulgaria and charged forward through mid-Serbia reached to Beograd almost the same time that other troops which advanced through the plain of Slavonia, although mountainous terrain in southeast Yugoslavia gave the defender a certain advantage over highly mechanized attack force.
The author thinks that the Kingdom still had a prospect to continue to resist even after its formal capitulation. However, the royal government deserted the country so hasty that it lost the public confidence and ultimately precluded the possibility to rebuild the nation after the War.