=) alright
I happen to know that Poland had bugged Lithuania for a while before the Union actually happened~
ref wiki~
"There were long discussions before signing the treaty, as Lithuanian magnates were afraid of losing much of their powers, since the union would make their legal status equal to that of the much more numerous Polish lower nobility. However Lithuania had been increasingly on the losing side of the Muscovite-Lithuanian Wars and by the second half of the 16th century it faced the threat of total defeat in the Livonian war and incorporation into Russia. The Polish nobility (the szlachta) on the other hand were reluctant to offer help to Lithuania without receiving anything in exchange. Still, the Polish and Lithuanian elite strengthened personal bonds and had opportunities to plan their united futures during increased military cooperation in the 1560s.[3] Sigismund II Augustus, King of Poland and Grand Duke of Lithuania, seeing the threat to Lithuania and eventually to Poland, nonetheless pressed for the union, gradually gaining more followers until he felt enough support to forcibly evict landowners in Ukraine who opposed its transition from Lithuania to Poland.[3] A clear motivation for Sigismund is that he was the last Jagiello and had no children nor brothers who could inherit the throne. So the Union was an attempt to preserve the continuity of his dynasty's work since the personal (but not constitutional) union of Poland and Lithuania at the marriage of Jadwiga of Poland and Wladyslaw II Jagiello. The Union was one of the constitutional changes required to establish a formal elected monarchy that would simultaneously reign over the two domains."