Croatia officially the Republic of Croatia is a country in Central Europe and Southeastern Europe at the crossroads of the Pannonian Plain the Balkans and the Adriatic Sea. Its capital and largest city is Zagreb. Croatia borders Slovenia to the north Hungary to the northeast Bosnia and Herzegovina to the southeast Serbia to the east and Montenegro to the southeast. The Croats arrived in the early 7th century in what today is Croatia. They organized the state into two dukedoms.