The study focuses on describing early medieval Croatia from the arrival of the Croats in the regions that are presently inhabited up until the establishment of the alliance between the Croatian and Hungarian kingdoms. Several theories exist regarding the arrival of the Croats, attempting to unravel their origins and the settlement of the Adriatic coast. During the initial centuries following their migration, the Croats predominantly lived in tribes that formed tribal alliances. In their endeavor to organize life in the new environment, the Croats came into contact with Byzantium and the still-fragmented West, encountering Christianity for the first time. The process of Christianization of the Croats and other peoples was a protracted one, spanning centuries after their migration. Byzantium and the Frankish state played significant roles in this process, with the latter expanding its borders to the territory of present-day Croatia in the 8th century. Croatia found itself at the crossroads between the Frankish and Byzantine empires, greatly influencing its subsequent development and the establishment of the first duchies. Through the establishment of these initial duchies, the Croats gradually unified as a people, enabling their involvement in shaping the European politics of that era. Consequently, Croatian dukes gained increasing autonomy, and by the end of the 9th century, the Pope acknowledged the authority of the Croatian ruler, marking Croatia's first international recognition as a country. Shortly after this recognition, the Croats united their lands into a kingdom that managed to endure for almost two centuries. The period of Croatian kings marked a golden age for Croatia until 1102, when it entered into an alliance with Hungary.