The Battle of Vukovar was an 87-day siege of Vukovar in eastern Croatia by the Yugoslav People's Army (JNA), supported by various paramilitary forces from Serbia, between August and November 1991. Before the Croatian War of Independence the Baroque town was a prosperous, mixed community of Croats, Serbs and other ethnic groups. As Yugoslavia began to break up, Serbia's President Slobodan Milošević and Croatia's President Franjo Tuđman began pursuing nationalist politics. In 1990, an armed insurrection was started by Croatian Serb militias, supported by the Serbian government and paramilitary groups, who seized control of Serb-populated areas of Croatia. The JNA began to intervene in favour of the rebellion, and conflict broke out in the eastern Croatian region of Slavonia in May 1991. In August, the JNA launched a full-scale attack against Croatian-held territory in eastern Slavonia, including Vukovar.

The Croatian National Guard was an armed force established by Croatia in April and May 1991 during the Croatian War of Independence. Although it was established within the framework of the Ministry of the Interior for legal reasons, the ZNG was under the direct command of the Ministry of Defence. It was tasked with the protection of Croatia's borders and territory, and with tasks normally associated with police forces. The ZNG was formed with the transfer of special police units to the ZNG, establishing four all-professional brigades in May 1991, and was presented to the public in a military parade in Zagreb on 28 May. It was commanded by Defence Minister General Martin Špegelj before his resignation in early August. Špegelj was replaced by General Anton Tus, who became the first head of the General Staff of the Armed Forces of the Republic of Croatia.