February 28th 1870 the BG autocephalous church was restated as an Exarchate by a Sultan’s official decree. That act confirmed the BG nationality living within the b orders of the Exarchate.
Here is the history of that important act:
In 1762, St. Paissiy of Hilendar (1722-1773), a monk from the south-western Bulgarian town of Bansko, wrote a short historical work which, apart from being the first work written in the Modern Bulgarian vernacular, was also the first ardent call for a national awakening. In History of Slav-Bulgarians, Paissiy urged his compatriots to throw off the subjugation to the Greek language and culture. The example of Paissiy was followed by a number of other awakeners, including St. Sophroniy of Vratsa (Sofroni Vrachanski) (1739-1813), hieromonk Spiridon of Gabrovo, hieromonk Yoakim Kurchovski (+1820), hieromonk Kiril Peichinovich (+1845).
The result of the work of Paissiy and his followers began before long to give fruit. Discontent with the supremacy of the Greek clergy started to flare up in several Bulgarian dioceses as early as the 1820s. It was not, however, until the 1850 that the Bulgarians initiated a purposeful struggle against the Greek clerics in a number of bishoprics demanding their replacement with Bulgarian ones. By that time, most Bulgarian religious leaders had realised that any further struggle for the rights of the Bulgarians in the Ottoman Empire could not succeed unless they managed to obtain at least some degree of autonomy from the Patriarchate of Constantinople. As the Ottomans identified nationality with religion and the Bulgarians were Eastern Orthodox, they were automatically added to the “Roum-Milet”, i.e., the Greeks. Thus, if the Bulgarians wanted to have Bulgarian schools and liturgy in Bulgarian, they needed an independent ecclesiastical organisation.
Borders of the Bulgarian Exarchate (1870-1912): bishoprics (in red) and vicariates (red diagonal stripes)The struggle between the Bulgarians, led by Neofit Bozveli and Ilarion Makariopolski, and the Greeks intensified throughout the 1860s. As the Greek clerics were ousted from most Bulgarian bishoprics at the end of the decade, the whole of northern Bulgaria, as well as the northern parts of Thrace and Macedonia had, by all intents and purposes, seceded from the Patriarchate. In recognition of that, the Ottoman government restored the once unlawfully destroyed Bulgarian Patriarchate under the name of "Bulgarian Exarchate" by a decree (firman) of the Sultan promulgated on February 28th, 1870. The original Exarchate extended over present-day northern Bulgaria (Moesia), Thrace without the Vilayet of Adrianople, as well as over north-eastern Macedonia. After the Christian population of the bishoprics of Skopje and Ohrid voted in 1874 overwhelmingly in favour of joining the Exarchate (Skopje by 91%, Ohrid by 97%), the Bulgarian Exarchate became in control of the whole of Vardar and Pirin Macedonia. The Exarchate was also represented in the whole of southern Macedonia and the Vilayet of Adrianople by vicars. Thus, the borders of the Exarchate included all Bulgarian districts in the Ottoman Empire.
The decision on the secession of the Bulgarian Orthodox Church was far from well accepted by the Patriarchate of Constantinople which promptly declared the Bulgarian Exarchate schismatic and declared its adherents heretics. Although there was nothing non-canonical about the status and the guiding principles of the Exarchate, the Patriarchate argued that “surrender of Orthodoxy to ethnic nationalism” was essentially a manifestation of heresy.
The first Bulgarian Exarch was Antim I who was elected by the Holy Synod of the Exarchate in February, 1872. He was discharged by the Ottoman government immediately after the outbreak of the Russo-Turkish War, 1877-78 on April 24, 1877, and was sent into exile in Ankara. Under the guidance of his successor, Joseph I, the Exarchate managed to develop and considerably extend its church and school network in the Bulgarian Principality, Eastern Rumelia, Macedonia and the Adrianople Vilayet. In 1895, the Tarnovo Constitution formally established the Bulgarian Orthodox Church as the national religion of the nation. On the eve of the Balkan Wars, in Macedonia and the Adrianople Vilayet alone, the Bulgarian Exarchate disposed of seven dioceses with prelates and eight more with acting chairmen in charge and 38 vicariates, 1,218 parishes and 1,212 parish priests, 64 monasteries and 202 chapels, as well as of 1 373 schools with 2,266 teachers and 78,854 pupils.
After World War I, by virtue of the peace treaties, the Bulgarian Exarchate was deprived of its dioceses in Macedonia and Aegean Thrace. Exarch Joseph I transferred his offices from Istanbul to Sofia as early as 1913. After the death of Joseph I in 1915, the Bulgarian Orthodox Church was not in a position to elect its regular head for a total of three decades.
Info taken by Wikipedia - The History of BG Orthodox Church