The co-chairs of the International Conference on the Former Yugoslavia, David Owen and Thorvald Stoltenberg, were closely involved in the political process surrounding the plan.
The document was prepared in the final months of 1994 and early 1995 before being presented to Croatian President Franjo Tuđman and the leaders of the self-declared Republic of Serbian Krajina (RSK) on 30 January 1995.
Three more attempts to revive the plan were made after Operation Flash in early May, when Croatia captured a portion of western Slavonia previously controlled by the RSK.
The first initiative, that began later that month, failed because the RSK demanded that the Croatian forces pull back from western Slavonia (which Croatia declined to do).
The final round of negotiations where the Z-4 Plan was proposed by international diplomats occurred in early August, when a major Croatian attack against the RSK seemed imminent.
On 4 August, Croatia launched Operation Storm, defeated the RSK and effectively ended the political process which led to the creation of the Z-4 Plan.
Further negotiations produced agreements on reopening a section of the Zagreb–Belgrade motorway (crossing the RSK-held part of western Slavonia, the Adria oil pipeline and several water-supply lines) by the end of 1994.
[17] It was a well-developed legal document[18] intended as the basis for negotiations and, according to Ahrens, designed to commit Croatia to an internationally agreed settlement and prevent it from turning to a military resolution of the war[19] (while being generous to the Croatian Serbs).
Part One defined Krajina as an autonomous region of Croatia, with borders based on the results of the 1991 Croatian census[19] (which identified eleven municipalities with an absolute Serb majority).
The region would have its own president, cabinet, legislation, courts, police force, emblem, flag and currency, and the right to levy taxes and make international agreements.
Over this period, International Conference on the Former Yugoslavia (ICFY) co-chairs David Owen and Thorvald Stoltenberg requested amendments to the plan and opposed its presentation to Croatian or RSK authorities.
[27] According to Florence Hartmann, in October representatives of Tuđman and those of Serbian president Slobodan Milošević met in Graz, Austria to discuss the proposed reintegration of the RSK into Croatia and their opposition to the Z-4 Plan.
[28] Tuđman disliked the plan because it envisaged a Serb state in Croatia, while Milošević saw it as a dangerous precedent that could be applied to majority non-Serb or ethnically mixed regions of rump Yugoslavia, such as Kosovo, Vojvodina and the Sandžak.
The maps were considered provisional because of concerns that the inclusion of Benkovac in Krajina would be contested by Croatia; a portion of the municipality had been predominantly inhabited by Croats, and it was on the Adriatic coast.
[33] On 12 January, shortly before the plan's final version was drafted, Tuđman announced in a letter to the UN that Croatia would not grant an extension of the UN peacekeeping mandate beyond 31 March and United Nations Protection Force (UNPROFOR) troops deployed to the RSK would have to leave.
Martić refused to receive the draft before the UN Security Council issued a written statement extending the UNPROFOR mandate to protect the RSK.
Kerestedjiants and Ahrens suggested that Martić should acknowledge receipt of the plan and then say that the RSK would not negotiate before the UNPROFOR issue was resolved, but he refused.
The meeting was attended by Owen, Stoltenberg, Galbraith, Kerestedjiants, Eide and Ahrens as the international diplomats; the RSK was represented by Martić, Mikelić and Babić, and the Croatian delegation was led by Šarinić.
[40] A second attempt to revive the plan arose from talks between Kinkel and French foreign minister Hervé de Charette on 28 June.
[41] Another effort involving the plan came about after Milošević asked the United States to stop an imminent Croatian attack against the RSK on 30 July.
Although in his request he indicated that negotiations should be held based on the Z-4 Plan, he refused to meet Galbraith (who wanted Milošević to pressure the RSK into accepting it) on 2 August.
He told Babić that the RSK could not expect international sympathy because of its involvement in the Siege of Bihać, and they would have to accept Croatian terms to avoid war.
[46] At the meeting the RSK insisted on the withdrawal of the HV from western Slavonia and the gradual implementation of a ceasefire, followed by economic cooperation before a political settlement was discussed.
By early October the process led to the Erdut Agreement, establishing a framework for restoring eastern Slavonia to Croatian rule.
[53] The Z-4 Plan was again resurrected in 1999 as a template for the Rambouillet Agreement, a proposed peace treaty negotiated between FR Yugoslavia and ethnic Albanians living in Kosovo.
[54] That year an "RSK government-in-exile" was set up in Belgrade, demanding the revival of the Z-4 Plan in Croatia (a move condemned by Drašković and Serbian President Boris Tadić).