Siemowit II of Masovia

In terms of foreign policy, Siemowit II tried to skillfully maneuver between his powerful neighbors: Władysław I the Elbow-high, the Teutonic Order, Lithuania and Bohemia.

[1] Later in that year, their youngest brother Wenceslaus concluded an alliance with the Teutonic Order; therefore, Władysław I attacked and plundered Płock; however this attack and destruction to a part of Masovia didn't bring the expected success: Siemowit II and his brothers, felt threatened by this action, decided to conclude an alliance with the Teutonic Knights on 2 January 1326 in the city of Brodnica, under which the Grand Master guaranteed the Masovian Dukes their independence and the integrity of their domains.

Moreover, the conflict created a permanent bond between the Masovian Dukes and the enemies of Władysław I - the Teutonic Knights and the Kingdom of Bohemia, and also bring another attack of the Polish King to the Duchy of Płock ub 1327 and the invasion of the Lithuanians to the domains of Siemowit II.

The conclusion of "eternal" peace between Poland and the Teutonic Order (signed in the Treaty of Kalisz on 8 July 1343) relieved Siemowit II, whose Duchy had an uncomfortable situation between the two powers.

As a potential successor Casimir III the Great on the throne of Poland, he also issued a document under which he agreed to waive the rights of Chełmno and Eastern Pomerania.