After the death of Batory in 1586, Zamoyski helped Sigismund III Vasa gain the Polish throne, fighting in the brief civil war against the forces supporting Habsburg archduke Maximilian III of Austria. The camp supporting Sigismund was rallied around Zamoyski, whereas Maximilian was supported by the Zborowski family. Zamoyski defended Kraków and defeated Maximilian's forces in the Battle of Byczyna in 1588. In that battle, which Sławomir Leśniewski describes as "one of the most important in Polish history, and the most important in Zamoyski's military career", Maximilian was taken prisoner and in the resulting Treaty of Bytom and Będzin of 1589 had to give up all pretenses to the Polish crown. Later that year Zamoyski proposed a reform of the royal elections, which failed to pass the Sejm. Zamoyski presented to this Sejm a project that in case the present King should die without issue none but a candidate of some Slav stock should henceforth be eligible to th Polish throne. This was a project which could even imagine the possibility of some kind of union between Catholic Poland, Orthodox Moscovy and semi-Protestant Bohemia. In fact, it was a circuitous and clumsy counter-proposal against pro-Habsburg policy.