On this very day 26th October 1377 Bosnian ruler Tvrtko I was crowned King and Bosnia became a kingdom.
The crowning took place at the Bosnian royal court Mile near today´s Visoko, Bosnia and Herzegovina.
During Tvrtko´s rule, Bosnia was the strongest country in the Balkans. In Bosnia was minted golden coins, which was 4 times larger than the Ottoman. Tvrtko bought the galley and Bosnia builds a strong navy.
Tvrtko Kotromanić was 15 years old when he inherited the Bosnian throne. In the first years of his government has sought to diminish the activity of the Catholic Church in Bosnia, as revealed in his correspondence with the lector of Djakovo diocese, which was discovered by Bishop Peter Siklos, and then the Hungarian King Louis I uses the offer from the Pope Innocent who gives permission for the crusade against the Bosnian cathars (bogomils). Hungary had launched a double invasion of the lands of Bosnia in 1363, but it suffered a heavy defeat and Tvrtko came out as the winner. This victory resulted in that Tvrtko in 1364 declared himself as the “Ban of Bosnia by the grace of God”(and not by the grace of Hungarian king Louis I).
Ban Tvrtko wanted to be crowned the Bosnian King (a title that could only be obtained from the Pope), but the Pope would not allow it, partly because of the Hungarian king. After the death of Serbian emperor Uros Nemanjic in 1371, Tvrtko appears as a pretender to the Serbian throne, claming kinship with Nemanjic family through the thin bloodline (the female line, through his grandmother). However, Tvrtko´s right of the Serbian crown was very little, because there were many other who had much closer kinship with Serbian Nemanjić family. In addition, Tvrtko Kotromanic was the ruler of Bosnia, a country and a family foreign to Serbs and he, Tvrtko, was only interested to strengthen the Bosnian state, which he had already proved in 1373 when he tore a part of Serbia and annexed it to the Bosnian state, after he defeated Serbian Duke Nichola Altomanović. Because Tvrtko´s chances to inherit the Serbian throne were small as the Serbian historian Sima Cirković writes: “..in any of the Serbian genealogy there is no mention of the ruler of the family Kotromanić..”, to increase his chances Tvrtko started the military campaings in the Serbian territory. Tvrtko´s main goal was to get an international recognition for himself as the King and for the Bosnian Crown.
After the death of Serbian emperor, as mentioned above, Serbia was in disarray, the war for power reigned between Serbian princes, and Tvrtko used this situation. Tvrtko decided to give a military help to the Serbian Prince Lazar against another Serbian duke Nichola Altomanović and also against the threat of the Hungarian king, who also pretended to the Serbian throne. In 1373 Tvrtko defeated Hungarian army from the west, and Lazar from the east, so Hungary emerges as a loser, and Tvrtko used this victory to take the Serbian crown. Shortly after Tvrtko decides to start the war against the Montenegrin ruler Georg Balšić and in 1377 the Bosnian army occupies cities of Trebinje, Dračevica, and the island Konavle. This victories encouraged Tvrtko to take the Serbian crown and split it, so he crowned himself with double crowns (“sugubi vijenac”) as the King of Bosnia, his native God-given country and as the King of Serbia. King Tvrtko also took titles from the Serbian throne and gave them to the Bosnian nobility.
Although he became ruler of the Serbian lands, Tvrtko was never recognized by the Serbian orthodox church, which always responded to prince Lazar when it came to church affairs.
After that, King Tvrtko turned towards the Adriatic coast and Croatian lands. Partly through wars, and partly through diplomacy King Tvrtko occupied cities of Split, Trogir, Šibenik and the islands of Brac, Hvar, Korcula, Šolta and Čiovo, which were put under the Bosnian Crown. So, after 1390 he was calling himself “King of Bosnia, Dalmatia, Croatia, Primorje and Raska”.