The Kingdom of Bulgaria was a historical state in Southeast Europe, established in 681 AD. It played a significant role in the region's development, particularly during the Middle Ages. The kingdom reached its peak under the rule of Tsar Simeon I, who expanded its territory and promoted the spread of Slavic culture and the Cyrillic alphabet. The kingdom experienced various periods of prosperity and decline, influenced by neighboring powers such as the Byzantine Empire and the Ottoman Empire. Ultimately, the Kingdom of Bulgaria was officially dissolved in 1946, transitioning to a people's republic after World War II.