The agreement fell apart in October after a number of events including the assassination of Blaž Kraljević, leader of Croatian Defence Forces (HOS) in Bosnia and Herzegovina, the fall of the areas of Posavina, Bosanski Brod, and Jajce into the hands of the Army of Republika Srpska (VRS), and after a major battle broke out between the HVO and the ARBiH in Prozor.

In 1990 and 1991, Serbs in Croatia and in Bosnia and Herzegovina had proclaimed a number of "Serbian Autonomous Regions" with the intent of later unifying them to create a Greater Serbia.

[4] On 25 March 1991, Franjo Tuđman met with Serbian president Slobodan Milošević in Karađorđevo, reportedly to discuss partition of Bosnia and Herzegovina.

[5][6] In November, the autonomous Croatian Community of Herzeg-Bosnia (HZ-HB) was established, it claimed it had no secessionary goal and that it would serve a "legal basis for local self-administration".

"[8] In April 1992, the siege of Sarajevo began, by which time the Bosnian Serb-formed Army of Republika Srpska (VRS) controlled 70% of Bosnia and Herzegovina.

[3] The Croatian Defence Forces (HOS), led by Blaž Kraljević in Bosnia and Herzegovina, which "supported Bosnian territorial integrity much more consistently and sincerely than the HVO" was also created.

[3] On 15 April 1992, the multi-ethnic Army of the Republic of Bosnia and Herzegovina (ARBiH) was formed, with slightly over two-thirds of troops consisting of Bosniaks and almost one-third of Croats and Serbs.

[12] Tuđman's Croatian Democratic Union (HDZ) party held important positions in the Bosnian government including the premiership and the ministry of defence, but despite this carried out a separate policy and refused for the HVO to be integrated into ARBiH.

[10] In January 1992, Tuđman had arranged for Stjepan Kljuić, president of the Croatian Democratic Union of Bosnia and Herzegovina (HDZ BiH) who favored cooperating with the Bosniaks towards a unified Bosnian state, to be ousted and replaced by Mate Boban, who favored Croatia to annex Croat-inhabited parts of Bosnia and Herzegovina.

He received an ultimatum from Boban warning that if he did not proclaim a confederation with Tuđman that Croatian forces would not help defend Sarajevo from strongholds as close as 40 kilometres (25 mi) away.

[21] In June and July, Boban increased pressure "by blocking delivery of arms that the Sarajevo government, working around a United Nations embargo on all shipments to the former Yugoslavia, has secretly bought.

[28] Cooperation was inharmonious, but enabled the transportation of weapons to ARBiH through Croatia in spite of the UN sanctioned arms embargo,[3] reopening channels blocked by Boban.

This was criticized as Croatian attempts at "claiming broader political and territorial rights in the parts of Bosnia and Herzegovina where large numbers of Croats live".

[34] The HOS's advance into eastern Herzegovina and occupation of Trebinje angered Boban who had affirmed to Karadžić that Croat forces were uninterested in the region.

Božidar Vučurević, the war-time mayor of Trebinje, stated he safeguarded records showing that SDS and HDZ figures considered it a "task" that need to be carried out.

[39] The dominant Croatian–Bosnian defense of Posavina fell apart after Tuđman and/or Gojko Šušak[40][41] ordered the withdrawal of the Croatian Army (HV), enabling the Serbs to gain control of the corridor and connect their captured territories in western and eastern Bosnia.