quality:corruption
Kingdom of Lithuania

Mindaugas, the duke of southern Lithuania, was among the five senior dukes mentioned in the treaty with Galicia–Volhynia. The Livonian Rhymed Chronicle, reports that by the mid-1230s, Mindaugas had acquired supreme power in the whole of Lithuania. In 1236, the Samogitians, led by Vykintas, defeated the Livonian Order in the Battle of Saule. The Order was forced to become a branch of the Teutonic Knights in Prussia, making Samogitia, a strip of land that separated Livonia from Prussia, the main target of both orders. The battle provided a break in the wars with the Knights, and Lithuania exploited this situation, arranging attacks on the Ruthenian provinces and annexing Navahrudak and Hrodna.

In 1248, a civil war broke out between Mindaugas and his nephews Tautvilas and Edivydas. The powerful coalition against Mindaugas included Vykintas, the Livonian Order, Daniel of Galicia and Vasilko of Volhynia. Taking advantage of internal conflicts, Mindaugas allied with the Livonian Order. He promised to convert to Christianity and exchange some lands in western Lithuania in return for military assistance against his nephews and the royal crown. In 1251, Mindaugas was baptized and Pope Innocent IV issued a papal bull proclaiming the creation of the Kingdom of Lithuania. After the civil war ended, Mindaugas was crowned as King of Lithuania on 6 July 1253, starting a decade of relative peace. Mindaugas later renounced Christianity and converted back to paganism. Mindaugas tried to expand his influence in Polatsk, a major centre of commerce in the Daugava River basin, and Pinsk. The Teutonic Knights used this period to strengthen their position in parts of Samogitia and Livonia, but they lost the Battle of Skuodas in 1259 and the Battle of Durbe in 1260. This encouraged the conquered Semigallians and Old Prussians to rebel against the Knights.

Encouraged by Treniota, Mindaugas broke the peace with the Order, possibly reverted to pagan beliefs. He hoped to unite all Baltic tribes under the Lithuanian leadership. As military campaigns were not successful, the relationships between Mindaugas and Treniota deteriorated. Treniota, together with Daumantas of Pskov, assassinated Mindaugas and his two sons, Ruklys and Rupeikis, in 1263. The state lapsed into years of internal fighting.