The Travel of the Croats.

From Ancient Persia (Iran) towards the Caspian Sea, Caucasus and to White Croatia (tribe of Slavic Croats which encompassed Czechia, Hungary, Poland, Ukraine) - size debatable and they finally created a duchy state on the Adriatic Sea on the land that was given to them by the Byzantine Empire to help with defeating the Avar Khagante. It included modern Croatian land, all of Bosnia and Red Croatia. The Duchy became a Kingdom and the first king of the Croatian Kingdom was Tomislav which made Croatia the biggest it was if we incl. vassal lands.