The Polish Lithuanian Commonwealth was partitioned by the Germans, Austrians, and Russians. But since both countries have gained their independence. What has stopped them from reforming their commonwealth, and is it even something the two countries want?
Not to discourage further discussion, but this earlier answer from u/yodatsracist (proving very useful today, second time I've linked it) may help with your question.
Why is Lithuania such a small country?
Also see the more recent answer by u/Pseudohistorian to Why did Lithuania get so little land after it's independence in 1918, considering it's great territory as Grand duchy of Lithuania?