The coronation and the alliance with the Livonian Order allowed for a period of peace between Lithuania and Livonia. During that time, the Lithuanians expanded east, while Livonia attempted to conquer Samogitia. Enticed by his nephew Treniota, Mindaugas broke the peace after the Order was defeated in the Battle of Skuodas in 1259 and the Battle of Durbe in 1260. Lithuanian forces were, however, unable to prevent the devastating Mongol invasion of Lithuania in 1258–1259. Treniota's influence grew as he waged a war against the Order and his priorities began to diverge from those of Mindaugas. The conflict resulted in the assassination of Mindaugas and two of his sons in 1263. The country reverted to paganism and its status as a kingdom was lost. The state survived as the Grand Duchy of Lithuania and the subsequent monarchs are known as Grand Dukes as they could not be crowned Kings until they converted to Christianity (the Christianization of Lithuania occurred only in 1387).