Boleslaw III, together with his ally King Coloman of Hungary, invades Bohemia in 1107 in order to aid Svatopluk the Lion of Bohemia in gaining the Czech throne.

The intervention in the Czech succession is meant to secure Polish interests to the south.

The expedition is a complete success.

On May 14, Svatopluk is made Prince of Bohemia, in Prague.

Boleslaw undertakes a punitive expedition against his brother Zbigniew later in 1107.

The reason for this is that Zbigniew had not followed the orders of Bolesław III and had not burned down the fort of Kurów.Another reason is that Zbigniew had not discharged his duty as a vassal and had not provided military aid to his lord, Bolesław III, for a campaign against the Pomeranians.

In the winter of 1107–1108, with the help of Kievan and Hungarian allies, Boleslaw III begins a final campaign to rid himself of Zbigniew.

His forces attack Mazovia, and quickly force Zbigniew to surrender.

Following this action, Zbigniew is banished from the country altogether.

From this point forward, Boleslaw III is the sole lord of the Polish lands, though in fact his overlordship begins in 1107 when Zbigniew pays him homage as his feudal lord.