Casimir, aided by his Kievan brother-in-law Vladimir, had started a war against Masovia in 1047 and seized the land.
It is probable that he also defeated Mieclaw's allies from Pomerania and attached Gdańsk to Poland.
This had secured his power in central Poland.
Three years later, against the will of the Emperor, Casimir had seized Bohemian-controlled Silesia, thus securing most of his father's domain.
The Emperor had ruled in 1054 in Quedlinburg that Silesia was to remain in Poland in exchange for a yearly tribute of one hundred and seventeen kilograms of silver and seven kilograms of gold.
Casimir had at that time focused on internal matters.
To strengthen his rule, he had re-created the bishopric in Kraków and Wrocław and erected the new Wawel Cathedral.
During Casimir's rule heraldry has been introduced into Poland and, unlike his predecessors, he promotes landed gentry over the drużyna as his base of power.
One of his reforms is the introduction, to Poland, of a key element of feudalism: the granting of fiefdoms to his retinue of warriors, thus gradually transforming them into medieval knights.
Following the death of Casimir in 1058, Boleslaw II, as the eldest son, inherits Greater and Lesser Poland as well as the Mazovian, Pomeranian, and Silesian lands.
His younger brothers Władyslaw Herman and Mieszko become governors of the remaining provinces.
