Arbitration Commission of the Peace Conference on Yugoslavia
On 20 November 1991 Lord Carrington asked: "Can the internal boundaries between Croatia and Serbia and between Bosnia and Herzegovina and Serbia be regarded as frontiers in terms of public international law?" Applying the principle of "uti possidetis juris", the commission concluded on 11 January 1992, "The boundaries between Croatia and Serbia, between Bosnia and Herzegovina and Serbia, and possibly other adjacent independent states may not be altered except by agreement freely arrived at... Except where otherwise agreed, the former boundaries become frontiers protected by international law".
Breakup of Yugoslavia
With the Plitvice Lakes incident of late March/early April 1991, the Croatian War of Independence broke out between the Croatian government and the rebel ethnic Serbs of the SAO Krajina (heavily backed by the by-now Serb-controlled Yugoslav People's Army). On 1 April 1991, the SAO Krajina declared that it would secede from Croatia. Immediately after Croatia's declaration of independence, Croatian Serbs also formed the SAO Western Slavonia and the SAO of Eastern Slavonia, Baranja and Western Srijem. These three regions would combine into the Republic of Serbian Krajina (RSK) on 19 December 1991.