It was launched on 10 June 1942, with the goal to encircle and destroy the Partisans who were operating in the Kozara mountain region near Banja Luka, which threatened German access to the Belgrade-Zagreb railway.

The offensive was a coup de main operation, which utilized direct action by elements of the Wehrmacht, Home Guard and Ustaše.

The Germans and their allies encircled the main group and achieved their objectives after nearly 40 days of bloody combat, with heavy casualties on both sides.

Most of the civilians were killed during or after the battle, others were sent to concentration camps such as Jasenovac, Stara Gradiška, Sajmište, or forced labor mines in German occupied Norway where many perished.

Both groups initially collaborated against the Axis, however differing policies and moral codes eventually led to a guerrilla war between the two movements.

The Ustaše commander Vjekoslav Luburić sent out a plan for a "security belt" around the river Sava and gave orders to round up the Serb population that was seen as supportive of the Partisans.

In April 1942, he formed his own Chetnik division and staged a coup at a hospital near Banja Luka, killing several Partisans including physician Mladen Stojanović.

The Germans were able to catch the exhausted Partisans by surprise and managed to capture Prijedor and the mines of Ljubjina, which were under danger of falling into enemy hands.

On 26 June, reinforcements from the 704th German Division to lay siege on the encircled Partisans and the 1st Krajina Detachment was ambushed during a break out attempt.

The Kozara Offensive became a part of national mythology in post-war Yugoslavia, which honored the bravery and martyrdom of the Partisans and people caught in the crossfire.

Large number of Serbs were killed on the spot, women and children were deported to the Jasenovac or Stara Gradiška concentration camps were many subsequently died.

Male prisoners were taken to the Nazi Sajmište concentration camp near Zemun in Belgrade or to forced labor mines in German occupied Norway from which few returned.