The siege of Mostar was fought during the Bosnian War first in 1992 and then again later in 1993 to 1994. Initially lasting between April 1992 and June 1992, it involved the Croatian Defence Council (HVO) and the Army of the Republic of Bosnia and Herzegovina (ARBiH) fighting against the Serb-dominated Yugoslav People's Army (JNA) after Bosnia and Herzegovina declared its independence from Yugoslavia. That phase ended in June 1992 after the success of Operation Jackal, launched by the Croatian Army (HV) and HVO. As a result of the first siege around 90,000 residents of Mostar fled and numerous religious buildings, cultural institutions, and bridges were damaged or destroyed.
As the wider conflict matured and the political landscape changed, the Bosnian Croats and Bosniaks began to fight against each other, culminating in the Croat–Bosniak War. Between June 1993 and April 1994 the HVO besieged Bosniak-concentrated East Mostar, resulting in the deaths of numerous civilians, a cut off of humanitarian aid, damage or destruction of ten mosques, and the blowing up of the historic Stari Most bridge. Hostilities ended with the signing of the Washington Agreement in March 1994 and the establishment of the Croat–Bosniak federation.
Background
In 1990 and 1991, Serbs in Croatia and in Bosnia and Herzegovina had proclaimed a number of "Serbian Autonomous Regions". Serbs used the well equipped Yugoslav People's Army (JNA) in defending these territories. As early as September or October 1990, the JNA had begun arming Bosnian Serbs and organizing them into militias. By March 1991, the JNA had distributed an estimated 51,900 firearms to Serb paramilitaries and 23,298 firearms to Serbian Democratic Party (SDS). The Croatian government began arming Croats in the Herzegovina region in 1991 and in the start of 1992, expecting that the Serbs would spread the war into Bosnia and Herzegovina. It also helped arm the Bosniak community. From July 1991 to January 1992, the JNA and Serb paramilitaries used Bosnian territory to wage attacks on Croatia. During the war in Croatia, Bosnian president Alija Izetbegović gave a televised proclamation of neutrality, stating that "this is not our war", and the Sarajevo government wasn't taking defensive measures against a probable attack by the Bosnian Serbs and the JNA.
On 25 March 1991, Croatian president Franjo Tuđman met with Serbian president Slobodan Milošević in Karađorđevo, reportedly to discuss the partition of Bosnia and Herzegovina. In November, the autonomous Croatian Community of Herzeg-Bosnia (HZ H-B) was established, it claimed it had no secessionary goal and that it would serve a "legal basis for local self-administration". It vowed to respect the Bosnian government under the condition that Bosnia and Herzegovina was independent of "the former and every kind of future Yugoslavia." Mate Boban was established as its president. In December, Tuđman, in a conversation with Bosnian Croat leaders, said that "from the perspective of sovereignty, Bosnia-Herzegovina has no prospects" and recommended that Croatian policy "support for the sovereignty [of Bosnia and Herzegovina] until such time as it no longer suits Croatia."
After the JNA's participation in the Croatian War of Independence, JNA units were regarded as an occupation force by the Croats of Mostar. It was perceived as a force friendly to the Serbs and hostile to Croats and Bosniaks (Bosnian Muslims). On 4 February 1992, local Croat citizens blockaded the roads from Mostar to Čitluk and Široki Brijeg in protest over the behavior of JNA reservists in the area. On 6 February Serbs blockaded the road from Mostar to Sarajevo. On 29 February and 1 March 1992 an independence referendum was held in Bosnia and Herzegovina. Independence was strongly favored by Bosniak and Bosnian Croat voters, while Bosnian Serbs largely boycotted the referendum. The majority of voters voted for independence and on 3 March 1992 president Alija Izetbegović declared independence from Yugoslavia, which was immediately recognised by Croatia.