 On 23 and 24 June , spontaneous mass gatherings occurred at several villages in the Gacko and Nevesinje districts . These rallies were prompted by the news of the German invasion of the Soviet Union , and those attending them voted to fight against the Ustaše . Professor <unk> <unk> Hoare states that the full @-@ scale uprising resulted from the Ustaše retaliation against attempts of the Serbs of eastern Herzegovina to defend themselves , combined with the launching of the German invasion on 22 June . At dawn on 24 June , the area of Nevesinje descended into full @-@ scale revolt , with around 400 armed rebels engaging the Home Guard garrison . By 24 June , the uprising had reached a massive scale across eastern Herzegovina , with between 1 @,@ 500 and 3 @,@ 000 armed rebels in total , including some Montenegrins . 
