Peace Process in Eastern Slavonia: Lessons for Conflict Resolution in Ukraine

The region of Eastern Slavonia, Baranja, and Western Sirmium witnessed intense conflict during the dissolution of Yugoslavia. Ethnic cleansing, displacement, and deep grievances shaped its turbulent history. Today, however, it stands as an example of successful post-conflict resolution. A combination of international mediation, local cooperation, and phased reintegration formed the backbone of the transition from war to peace in the Balkans during the 1990s. Considering the ongoing conflict in Ukraine, this case offers valuable lessons that could help guide efforts towards resolution and stability in Europe.

The analysis begins by exploring the diplomatic and political efforts of Serbia and Croatia that led to the Erdut Agreement (1995) and the peaceful reintegration of the disputed region into Croatia. It then offers a brief overview of current peace initiatives in Ukraine. Drawing on the Balkan experience, the final section suggests strategies for achieving a sustainable and equitable resolution to the war in Ukraine.

This article does not suggest that the two conflicts are entirely comparable. While certain parallels exist, particularly in the rhetoric of identity and narratives used by the aggressors, each conflict arises from distinct historical circumstances and geopolitical dynamics. Instead, the focus is on identifying actionable insights from the Eastern Slavonia model that could inform strategies for addressing the ongoing crisis between Ukraine and Russia.

Independence, Bloodshed and the Agreement

During the Croatian War of Independence (1991–1995), Eastern Croatia became a hotspot of the conflict when it was seized by ethnic Serb forces backed by the Yugoslav People's Army. Fear and polarisation, driven by antagonising national state-building projects, escalated ethnic tensions. The regions of Krajina and Slavonia, in particular, reflected this intensifying hostility.

At the time, ethnic Serbs made up about 15% of Croatia’s population, and for many of them, the occupation of the territory was seen as a means of protecting Serb lives and property. For Croats, on the other hand, it was perceived as deliberate aggression.

In 1995, Croatia retook the regions of Western Slavonia and Krajina through two military operations. Combined with successful NATO campaigns in Bosnia and Herzegovina, Serbian forces were nearing collapse. Fearing a third Croatian offensive, Serbia was compelled to enter negotiations, which led to the signing of the Erdut Agreement on 12 November 1995. The document provided a framework for the peaceful reintegration of Eastern Slavonia, Baranja and Western Sirmium into Croatia.

The Agreement established a 12-month transitional period and called on the United Nations (UN) Security Council to launch a Transitional Administration and deploy an international police force to carry out demilitarisation and organise local elections. It also included provisions for human rights protection. The UN Transitional Administration for Eastern Slavonia, Baranja and Western Sirmium (UNTAES) was notable for its emphasis on trust-building and its gradual implementation strategy, which allowed tensions to ease and cooperation to grow over time. By 1998, the region had been fully reintegrated into Croatia.

Enablers of Peace

The reintegration of Eastern Slavonia has been described by Boris Pavilić as the victory of reason over the victory of arms in a scenario marked by mutual distrust. National interests, external interference, fear of betrayal, and a divided public opinion all contributed to lingering doubts about a successful outcome. From the decision to negotiate to the holding of the first post-war elections, multiple factors proved essential to its success. In particular, military and diplomatic leverage helped overcome scepticism and enabled effective implementation.

For Serbia, the threat of further military defeats, the deterioration of military capabilities after the setbacks in Bosnia and Herzegovina (BiH), and the risk of increased international sanctions against Yugoslavia prompted a reassessment of its position. For Croatia, the decision to pursue a peaceful resolution was encouraged by the U.S. support for its interests. Coherent with President Clinton’s peace initiative for BiH, the country backed Croatia’s objective of restoring sovereignty over Eastern Slavonia. 

At the same time, the U.S. Ambassador to the UN Madeleine Albright expressed “deep concern about the development of the situation in Croatia and the complete American opposition to any military action in Eastern Slavonia.” On the European arena, Croatia’s bid for membership in the Council of Europe – and later, its accession to the EU – also depended on the peaceful solution for the conflict. 

Although the agreement did not erase mutual grievances, the reintegration was ultimately successful due to three key elements: strong international mediation, economic reconstruction measures, and meaningful civil society engagement.

International Mediator

The establishment of UNTAES under the leadership of General Jacques Paul Klein, along with the mission’s robust human and material resources, provided a neutral platform to create and train temporary police forces, to carry out demilitarisation of the area, and to build confidence among all ethnic communities. This effort was made possible due to the collaboration with willing local authorities, Ivica Vrkić, Vesna Škare-Ožbolt and Vojislav Stanimirović, that bridged differences between locals, allowing the return and life normalisation of displaced people. Combined, these aspects ensured that legitimacy and impartiality remained bases of the process.

Economic Provisions

Economic recovery played a vital role in stabilising the region and preventing renewed conflict. Key initiatives included demining populated and arable areas, rebuilding critical infrastructure and housing, and generating jobs. Apart from the illegal markets, another way of steering up the local economy was through disarmament, demobilisation and reintegration. Through a UNTAES-managed buy-back program financed by Croatia, civilians were encouraged to exchange their weapons for Deutsche Marks, injecting money into the local economy. This strategy also allowed the reintegration of ex-combatants into the labour market and increased their purchasing power.

Civil Society and Minorities

The involvement of local communities and assurance of minority rights were central to the reintegration effort. Collaboration between troops and local NGOs facilitated trust-building activities bringing together Serbs and Croats. One notable initiative was “Klein’s marketplace”, a commercial hub turned into a space for dialogue and reconciliation, facilitating interactions among citizens and exposing the mutual interest in ending the war. Trust was further reinforced through guarantees of linguistic rights, education access, and political representation for the Serb population; provided they accepted Croatian institutions and authority.

Achieving Peace in Ukraine

Unlike Eastern Slavonia, Ukraine's conflict involves far greater geopolitical stakes. Additionally, mutual distrust between Russia and Ukraine presents significant obstacles that will require persistent and creative diplomacy. 

Since February 2022, multiple attempts to end the conflict have been made, yet without success. Indirect negotiations and mediation efforts, including various international forums and actors, have resulted in a further deterioration of relations. Even establishing temporary ceasefires, essential for signalling genuine willingness to negotiate, has proven impossible.

Thus far, the parties have focused on their own national security concerns rather than addressing each other’s apprehensions. On one side, Russia demands total control of four oblasts (Luhansk, Donetsk, Zaporizhzhia and Kherson) to secure a land corridor to Crimea, and their legal recognition from Ukraine and the U.S. Ukraine, on the other hand, despite proposing neutrality in 2022, now defends territorial restoration of its 2014 borders. 

Amid these circumstances, analysts such as Samuel Charap and Sergey Radchenko have noted that certain contentious issues, including the status of occupied territories, sanctions relief for Russia, and funding for Ukraine’s postwar reconstruction, have been largely absent from formal negotiations. While these analysts suggest that raising such topics might help overcome diplomatic deadlock, engaging with them carries significant political and ethical risks, particularly the danger of legitimising territorial aggression. The inclusion of these issues in diplomatic discussions should therefore be viewed not as an endorsement of compromise, but as a recognition of the complex realities shaping any potential path to peace.

International Mediation

An important piece in this dynamic is effective mediation. Drawing from the Eastern Slavonia model, international pressure, be it military or diplomatic, influences not only the decision to negotiate, but also the outcome of the deal. In this dispute, actors that once played prominent roles are now reluctant to provide security guarantees or apply coordinated pressure on both sides. Western diplomacy, once central to conflict resolution efforts, now appears hesitant and fragmented.

The U.S. has indicated plans to reduce its military aid to Ukraine next year, suggesting that Europe should assume a greater share of the responsibility. Diplomatically, President Donald Trump has failed to offer a fast solution for the conflict after being elected, even though he considered supporting Putin’s demands by “de jure” recognising Crimea and “de facto” recognising other Russian-occupied territories. In fact, Trump’s transactional diplomacy has created new uncertainties to America’s historical allies and delayed the progress of the negotiations.

While the U.S. seems to disengage, European leaders reaffirmed their commitment to Kyiv by expanding defence budgets and supporting NATO members to do the same. The accession of Ukraine to the EU and the promise of long-term security guarantees, however, are more difficult to materialise. Another aspect to consider is whether the accession would bring peace to the country and the continent.

The fulfilment of internal reforms in terms of state functioning and economy are just the tip; the country depends on several external factors, concerning the proper end of the war and the reform of EU’s funding and decision-making system. Even so, geopolitically, Europe has the potential and the opportunity to lead both parties to a peaceful resolution.

What is it Missing?

Reflecting on the Eastern Slavonia experience, a key missing component is a credible international framework for enforcing transitional governance and phased demilitarisation. Unlike UNTAES, no neutral and empowered body has emerged to build trust and oversee implementation. Mediation efforts so far have lacked both legitimacy and enforcement capacity, and important actors remain reluctant to engage.

Battlefield momentum in Ukraine’s favour could renew interest from the U.S. and EU to re-engage in structured mediation, creating conditions for both parties to return to the negotiation table. As in the Balkan case, a sustainable peace process would require all sides to adhere to previously agreed principles, mainly Russia's recognition of Ukraine's sovereignty in both legal and practical terms. This remains a difficult demand, as Russia has repeatedly disregarded international agreements in both word and action.

For Ukraine, diversifying its economic and energy partnerships has become an important strategy for reducing long-term vulnerabilities. In this context, closer ties with the European Union have been viewed by some policymakers as a pathway to economic stabilisation and reduced future dependence on Russia. While such integration may offer potential benefits, it also presents political and technical challenges that would need to be carefully navigated in a volatile regional environment.

Still, the most difficult challenge remains the status of disputed territories. While proposals such as economic incentives for withdrawal, transitional governance, or joint administration may offer short-term compromises, they would require unprecedented political will, robust international guarantees, and sustained engagement to succeed; conditions that are unlikely in the current climate.

Challenges Ahead

Post-war recovery in Ukraine will face significant physical, social, and political obstacles. Demining, rebuilding infrastructure, and ensuring the safe return of displaced populations will demand sustained international support. Socially, restoring trust between divided communities, reintegrating Russian-speaking populations in contested areas, and promoting reconciliation should be in the centre of civil reconstruction. 

Post-war recovery in Ukraine will face significant physical, social, and political obstacles. Demining, rebuilding infrastructure, and ensuring the safe return of displaced populations will demand sustained international support.

Politically, the country must balance the pursuit of justice with the realities of reintegration. Moreover, Ukraine’s EU aspirations also hinge on resolving territorial disputes and strengthening governance – as well as on the EU's ability to enact its own reforms and politically align Member States. Finally, the fragile geopolitical environment means that leadership changes in the U.S. or EU could undermine progress. Lasting peace will require not only negotiations but continued commitment to rebuilding, accountability, and resilience at both national and international levels.

The peace process in Eastern Slavonia illustrates that even deeply entrenched conflicts can be resolved through inclusive diplomacy, phased reintegration, and sustained international engagement. While the war in Ukraine presents far greater geopolitical complexity, the lessons from the Balkans remain relevant. Durable peace will require more than military victories or ceasefire agreements. By drawing on past successes while adapting to new realities, a pathway toward a just and lasting peace in Ukraine remains possible.