Mieszko I of Poland and half a century later, by Bishop Thietmar of Merseburg. By the time Mieszko I took over from his father, the Polans' tribal federation of Greater Poland had for some time been actively expanding. Continuing this process, perhaps in the first years of Mieszko's reign, if it had not been done already by his father, Mieszko I conquered Masovia. Likely also during that period or earlier, at least partially Gdańsk Pomerania was obtained. Mieszko's interests were then concentrated mainly on areas occupied by the eastern (near the Oder River) branches of the Polabian Slavs; some of them became soon subordinated
Mieszko II the Fat and was succeeded by his son Henry II the Pious, who also assumed the regency over Opole-Racibórz. Shortly after, Mieszko II began to claim the government of their lands. It is unknown exactly when Mieszko II took over the rule over Opole-Racibórz, but this has been probably in late 1238 or early 1239 (who is more likely). One of the first politic decisions of Mieszko II was his marriage with Judith (b. 1222/25 – d. 4 December 1257/65?), daughter of Duke Konrad I of Masovia, who gave to the Duke of Opole-Racibórz greater autonomy in his rule. Mieszko II's mother