The First Bulgarian Empire was established in the late 7th century, around 681 AD, when the Bulgarian tribes united under the leadership of Asparuh. It became a significant political and cultural entity in Southeast Europe, expanding its territory to include parts of modern-day Bulgaria, Romania, and Serbia. The empire played a crucial role in the region's history, influencing trade and cultural exchanges. During its peak in the 9th and 10th centuries, the empire adopted Christianity as the state religion, which helped to unify the diverse population. The establishment of the Cyrillic alphabet by the disciples of Saints Cyril and Methodius further promoted literacy and culture, leaving a lasting legacy in the Slavic world.