Istria was annexed to the Kingdom of Italy in 19 December 1920 on the grounds of the Rapallo Treaty and the annexation law. At the same time, the first fascist organizations started to appear in Istria and a wave of fascist violence began. In 1921, the first major organized uprisings of the population against fascist terror occurred. The uprising of the peasants in Proština and the rebellion of miners known as the Labin Republic are particularly pivotal in this regard. In 1927, the first secret anti-fascist organizations Borba and TIGR were founded. With the beginning of World War II and the disintegration of the Kingdom of Yugoslavia, political emigrants who were members of the KPH returned to Istria and established first contacts. Soon after their arrival, the first institutions of the NOP and the First Istrian Partisan Company were founded. On 9 September 1943, a national uprising began, in which all of Istria except Pula was liberated in the span of a few days. On 2 October 1943, the German operation ''Wolkenbruch'' began, in which the partisan movement suffered heavy losses and after which Istria was again occupied. The partisan movement was reorganized and by the end of 1943, 13 partisan companies had been formed. In the final operations from the end of April to the beginning of May 1945, the whole of Istria was liberated by the 4th Army of the Yugoslav Army.