In subsequent years, Casimir I actively supported his father's turbulent politics, which brought him in 1242 to conquer the district of Wyszogród from the rulers of Gdańsk.

After this failure, Casimir I appealed to the Knights Templar, who settled in Łuków, in order to secure the northern border of his territory.

This expedition was a complete victory, and on 29 November 1259, Casimir I was forced to surrender and promised to cede Ląd to Bolesław the Pious.

Leszek II the Black, Casimir I's eldest son, took advantage of his father's difficult position and demanded his own district, using as an excuse the intrigues of his stepmother, who wanted to obtain more land for her own children.

As her dowry, she received the castellany of Ląd, which was the cause of the Casimir I's long conflict with the Duchy of Greater Poland.

As her dower, she received the district of Ruda, but the quick action of Przemysł I, Duke of Greater Poland, prevented this land from passing to the Masovian branch.