The Wehrmacht carried out mass executions of civilians in retaliation for resistance activity e.g., the Kragujevac massacre.
Hungarian occupation troops massacred civilians (mostly Serbs and Jews) during the a major raid in southern Bačka, under the pretext of suppressing resistance activities.
Finally, during and after the final stages of the war, Yugoslav authorities and Partisan troops carried out reprisals, including the deportation of the Danube Swabian population, forced marches and executions of thousands of captured soldiers and civilians fleeing their advance (the Bleiburg repatriations), atrocities against the Italian population in Istria (the Foibe massacres) and purges against Serbs, Hungarians and Germans associated with the fascist forces.
On the eve of the invasion, there were 165 generals on the Yugoslav active list. The terms of the capitulation were extremely severe, as the Axis proceeded to dismember Yugoslavia.
On 6 April 1941 the Kingdom of Yugoslavia was invaded from all sides by the Axis powers of Germany, Italy, and their ally Hungary.
During the invasion, Belgrade was bombed by the German air force (Luftwaffe).
Two of the principal constituent national groups, Slovenes and Croats, were not prepared to fight in defense of a Yugoslav state with a continued Serb monarchy.
The only effective opposition to the invasion was from units wholly from Serbia itself.Non-combat victims included the majority of the country's Jewish population, many of whom perished in concentration and extermination camps (e.g. The Croatian Ustaše regime committed genocide against Serbs, Jews, Roma and anti-Fascist Croats.