State Anti-Fascist Council for the National Liberation of Croatia

The State Anti-Fascist Council for the National Liberation of Croatia (Zemaljsko antifašističko vijeće narodnog oslobođenja Hrvatske), commonly abbreviated ZAVNOH, was first convened on 13–14 June 1943 in Otočac and Plitvice as the chief political representative body in World War II Axis-occupied Croatia (part of Yugoslavia at the time). It was dominated by the Communist Party of Croatia, a nominally-independent political party active in the territory largely corresponding to present-day Croatia. Despite its nominal independence, the party was a de facto branch of the Josip Broz Tito-led Communist Party of Yugoslavia. ZAVNOH also included representatives or former members of peasant organisations, trade unions, the Croatian Peasant Party, and the Independent Democratic Party.

In addition to performing day-to-day regulatory and government tasks in the territory held by Yugoslav Partisans within Croatia under the leadership of Andrija Hebrang, ZAVNOH sought to broaden the appeal of partisan resistance to the Croatian population by presenting it as not entirely communist. It also tried to reconcile Croat and Serb equality with the promotion of Croatia's interests, sometimes marginalising the Serbs and triggering conflict with Tito. At its third session, in Topusko, ZAVNOH upheld the decisions on federal post-war Yugoslavia adopted by the Anti-Fascist Council for the National Liberation of Yugoslavia. In 1945, ZAVNOH was renamed the People's Sabor of Croatia.

Its work, ideas and decisions contributed to the leadership programme of the League of Communists of Croatia, culminating in the 1971 Croatian Spring. ZAVNOH's decisions were then used to justify newly introduced policies seeking to reform the Yugoslav federation and promote Croatian interests. The 1990 Constitution of Croatia, adopted shortly before the declaration of Croatian independence, cites ZAVNOH in its preamble as a foundation of Croatian statehood.

Seeking retribution for their withdrawal from the Tripartite Pact after the March 1941 Yugoslav coup d'état, Adolf Hitler sought to destroy the Kingdom of Yugoslavia by dismembering it for annexation by Nazi Germany and its allies. The move was supported by Italian leader Benito Mussolini, who believed that it would help Fascist Italy expand their territory by absorbing former Yugoslav territories. German plans for the breakup of Yugoslavia also envisaged some form of autonomy for the Croats, exploiting Croatian dissatisfaction with the Yugoslav regime. Hitler offered Hungary the opportunity to absorb Croatia on 27 March 1941 (apparently referring to the territories largely corresponding to the former Kingdom of Croatia-Slavonia), but Regent Miklós Horthy declined his offer. Only days later, Germany determined to establish a Croatian puppet state.

The Nazis turned to the Croatian Peasant Party (Hrvatska seljačka stranka, HSS), the most popular Croatian political party at the time, to set up the state. They offered party leader Vladko Maček the opportunity to govern it, but Maček declined. Its rule was then reluctantly offered to the Italian-based Ustaše and their leader, Ante Pavelić. Mussolini sought to capitalise on the promises made in a 1927 memorandum submitted by Pavelić and Ivo Frank, promising territorial concessions to Italy. The Independent State of Croatia (Nezavisna Država Hrvatska, NDH) was declared on 10 April, as the Wehrmacht was approaching Zagreb. The declaration was made by Slavko Kvaternik at the urging of, and with support from, SS Colonel Edmund Veesenmayer of the Dienststelle Ribbentrop. Pavelić and the Ustaše were only permitted to leave Italy and Italian-occupied territory in Yugoslavia after Mussolini extracted a written confirmation of the 1927 pledge, allowing him to reach Zagreb in the early morning of 15 April with 195 Ustašas. Yugoslavia surrendered shortly thereafter, on 17 April 1941, with King Peter II and the government fleeing the country. The decision to abandon armed resistance to the Axis powers so early placed the Yugoslav government-in-exile in a poor position, further weakened by quarreling ministers who appeared united only in their opposition to communism.

With defeat imminent, the Communist Party of Yugoslavia (Komunistička partija Jugoslavije, KPJ) instructed its 8,000 members to stockpile weapons in anticipation of armed resistance (which spread throughout the country, except for Macedonia, by the end of 1941). Building on its experience in nationwide clandestine operation, the KPJ organised the Partisans into a resistance force led by Josip Broz Tito. The KPJ concluded that the German invasion of the Soviet Union had created favourable conditions for an uprising, and its politburo established the Supreme Headquarters of the National Liberation Army of Yugoslavia (Narodonooslobodilačka vojska Jugoslavije, with Tito its commander-in-chief) on 27 June 1941. In the territory largely corresponding to present-day Croatia, the Communist Party of Croatia (Komunistička partija Hrvatske, KPH) operated as a nominally-independent party but was a de facto KPJ branch; at the beginning of the war, it had 4,000 members.

The Serb population living in the NDH was eager to join the Partisan struggle, due to their severe persecution by the Ustaše regime. The KPJ competed for Serb loyalty with the Chetniks: nationalist Serb guerrillas who fought the Partisans and the NDH, backed by Fascist Italy and organised as the Anti-Communist Volunteer Militia. A major contributor to Croat Partisan recruitment was the transfer of a large portion of the Adriatic coast to Italy through the Treaties of Rome as fulfilment of Pavelić's promise to Mussolini. By late 1943, Croatia's contribution to the Yugoslav Partisan resistance was disproportionately large: 38 of its 97 brigades.

In November 1942, the Partisans captured the town of Bihać and secured a large part of western Bosnia, Dalmatia and Lika. On 26 and 27 November, the pan-Yugoslav Anti-Fascist Council for the National Liberation of Yugoslavia (Antifašističko vijeće narodnog oslobođenja Jugoslavije, AVNOJ) was established in Bihać at the urging of Tito and the KPJ. At its first session, the AVNOJ adopted a multi-ethnic federal state as the basis for the country's future government but did not determine the post-war system of government. The number of future federal units and their equality were ambiguous.