By the early twentieth century the country was once again embroiled in war; the Balkan wars of 1912 and 1913 impeded economic and social development in the country. Once again, as in the case of eastern Rumelia, irredentism was the Bulgarian motive for war. Both eastern Thrace and Macedonia, the lands ceded to Bulgaria by the Treaty of San Stefano, were still under Turkish rule. The lands had not only large Bulgarian populations but also strategic and economic significance. Macedonia, more than Thrace, was of extreme importance to Bulgaria; Bulgarians believed the population of Macedonia to be composed almost exclusively of Bulgarians. The issue of Macedonia was, in fact, a focal point around which Bulgarian political life revolved after 1878, because that issue was seen by the Bulgarians as involving the territorial integrity of their nation. Between the tenth and fourteenth centuries Macedonia was alternately occupied by the Bulgarians, the Serbs, and the Turks. At the time of liberation Macedonia was ceded to the Bulgarians by the Treaty of San Stefano, only to be returned to the Turks by the Treaty of Berlin. In 1893 the Internal Macedonian Revolutionary Organization (IMRO) was founded. This terrorist organization, with the battle slogan "Liberty or Death for Macedonia," fought a continual underground war of terrorism against the Turks. In 1903 there was a major Macedonian uprising in which two factions participated. Although the predominant faction favored Bulgarian annexation of Macedonia, another group favored complete autonomy for Macedonia. In 1908, when King Ferdinand proclaimed Bulgaria completely independent, memories of the medieval Bulgarian empire, which included Macedonia, were rekindled. The Balkan Wars The tumultuous history of Macedonia set the stage for the two Balkan wars. In 1912, at the onset of the First Balkan War, Serbia, Bulgaria, Montenegro, and Greece formed an alliance to drive the Turks from Europe. Turkey, who was at war with Italy at the time, was weak and disunited. Macedonia and Thrace were hotbeds of internal disorder. In October 1912 Turkey declared war on Serbia and Bulgaria, a move that was countered by a Greek declaration of war on Turkey. In 1913 the Bulgarians succeeded in capturing Adrianople, and the Greeks captured Salonica, Crete, and Samos. Eventually, the Turks were badly defeated. But the question of Macedonia remained. Serbia, Greece, and Bulgaria all laid claim to the land at the end of the first Balkan War. Eventually a compromise was reached: the northern section went to Serbia and the eastern section, to Bulgaria.