Original sentence: The columns were for the most part made-up of remnants of the Ustaše of the Independent State of Croatia (NDH) (a fascist puppet state of the Nazi regime in Germany, established in occupied Yugoslavia) and the remnants of the Chetnik movement (a collaborating royalist force, consisting of ethnic Serbs and Montenegrins).The remnants of the Ustaše military and the Chetniks (a collaborating Serbian nationalist movement) began to withdraw to the Austrian border on May 12, traveling to Bleiburg where the 38th British Infantry Brigade was stationed
Edited sentence: The columns were for the most part made-up of remnants of the Ustaše of the Independent State of Croatia (NDH) (a fascist puppet state of the Nazi regime in Germany, established in occupied Yugoslavia) and the remnants of the Chetnik movement (the Yugoslav royalist force, mainly consisting of ethnic Serbs and Montenegrins, which seemed to be collaborating that time), consisting of ethnic Serbs and Montenegrins).The remnants of the Ustaše military and the Chetniks (the Yugoslav royalist force, mainly consisting of ethnic Serbs and Montenegrins, whose collaborationism is higly disputed  Serbian nationalist movement) began to withdraw to the Austrian border on May 12, traveling to Bleiburg where the 38th British Infantry Brigade was stationed