What was the main feature of the Lithuanian state?

A feature of the Grand Duchy of Lithuania was that many rulers did not succeed. The Lithuanians united under their banners many tribes similar and different in culture and lifestyle. Lithuanians were warlike. Mindaugas could boast of titles that no monarch of Western Europe and Russia could claim. Lithuanians even owned the Kiev region. At that time, no state could resist this principality.
The main difference of this principality can be considered the unification of the lands, the beginning of the dynasty of Polish kings. Each king of the Commonwealth, ascending the throne, swore an oath of loyalty to the peoples: Lithuanian, Polish, Rusyns. In this case, the Rusyns are Ukraine.