Bulgarian relations with Yugoslavia were conditioned by old issues of Balkan politics and by strong domestic political forces at work in both countries. Throughout the 1980s, the Yugoslav media complained loudly that Bulgaria mistreated its Macedonian citizens by insisting that Macedonians were ethnically Bulgarians, making separate ethnic recognition inappropriate. The Zhivkov regime (and its successors), fearing that inflamed nationalism in Yugoslavia would intensify demands for Macedonian autonomy across the border in Bulgaria, largely ignored the Yugoslav propaganda campaign on the Macedonian issue. The dispute over Macedonia survived and prospered after communism lost its grip on both countries. Bulgarian nationalists, stronger after Zhivkov, held that the Slavic population of the Republic of Macedonia was ethnically Bulgarian, a claim leading naturally to assertion of a Greater Bulgaria. To defuse nationalist fervor on both sides, and in keeping with the policy of improved relations with all neighbors, Zhelev officially advocated nonintervention in the ethnic affairs of other nations.

The nonintervention strategy assumed greater importance when the Republic of Macedonia sought independence from the Yugoslav federation in 1991 in an effort to escape the increasing dominance of the Republic of Serbia in the federation. That effort reinforced the protective attitude of Macedonian nationalists in Bulgaria toward Yugoslav Macedonia, which had been part of Serbia in the interwar period. Serbia's use of force to prevent the breakup of the Yugoslav federation in 1991 triggered Bulgarian fears of wider destabilization in the Balkans if Serbian expansionism were fully revived.

In 1991 Bulgarian policy toward Yugoslavia was complicated by the rejuvenation of Macedonian national groups in Bulgaria. The largest of these was the Union of Macedonian Societies, a longstanding cultural and educational society that in 1990 took the prefix IMRO (Internal Macedonian Revolutionary Organization), which was the name of the terrorist organization active in Bulgaria, Greece, and Serbia between 1893 and 1935 (see The Macedonian Issue , ch. 1). But the threat posed by such groups remained small because the focus of Bulgarian nationalism was the Turkish issue in 1991, and because economic reform was the major concern of all factions. In spite of claims by the Serbian press that Bulgaria was aiding Croatia in the civil war of 1991 and that Bulgaria owed Serbia reparations from World War II, Bulgaria followed Zhelev's policy of nonintervention as the Yugoslav civil war continued.

Data as of June 1992