Croats of Bosnia and Herzegovina Dalmatian Croatia formed a united Croatian kingdom, which included Dalmatia and part of Bosnia and Herzegovina, Pannonia (eastern Slavonia and northeastern Bosnia), and Savia (western Slavonia). In 1102 Croatia entered into a union with the Kingdom of Hungary. After this, Bosnia, which was earlier part of the Kingdom of Croatia, started to disassociate with Croatia. At first, Bosnia became a separate principality under Ban Kulin who managed to solidify Bosnian autonomy at the expense of more powerful neighbours, but only in the 14th century did Bosnia become a formidable state. In the 14th century, King Tvrtko I conquered part of
Agreement on Friendship and Cooperation between Bosnia and Herzegovina and Croatia in the party between Croats from ethnically mixed areas of central and northern Bosnia and those from Herzegovina. Milivoj Gagro, prewar Croat mayor of Mostar and ally of Kljuić said: "The secessionist policy [union with Croatia] was consistently supported by the Herzegovina side, not by Sarajevo, Posavina, or Central Bosnia Croats. [...] Croats from Central Bosnia and Posavina, as well as those from urban centers who lived with Muslims and Serbs, thought differently. But when the war picked up, Posavina Croats were attacked, Sarajevo was surrounded [...] Kljuić was sidelined and Boban came in with idea [the Croat separatist idea]