Lithuania was ruled by many prominent and strong dukes prior to the Commonwealth. Most of the eastern territory (Ukraine, Belarus, parts of Moldova and Russia) were taken by strength, and it was relatively easy to do so, since many territories there were poorly managed and ruled, with scarce armies and bad administration. Several rulers of pre-Commonwealth Lithuania (specifically King Mindaugas, Gediminas) also acquired territories by diplomatic actions.

When the Commonwealth was formed, the territory got even bigger, but due to the differences between Lithuanian and Polish cultures, people living in the Commonwealth weren't prospering, mostly Lithuanians. Important institutions and administration was controlled by Poland, and thus polonisation started: People started talking Polish in Lithuania, public schools taught Polish etc. Because of this, Lithuania and Poland couldn't cooperate well and that was our Achilles heel during the 2nd German reich and Russian Empire times. The Commonwealth started to collapse, as whole territories were taken by either Germans or Russians. After the Commonwealth finally died, the only leftover Lithuanian territory was that of modern-day Lithuania, even smaller. Over time some small territories were taken back, but the Soviets occupied Lithuania and no further expansion could happen.