Complex sentence: Because he had no sons, he has concluded the Treaty of Kepno in 1282 making duke Przemysl II of Poland, his successor in all his possessions, what was confirmed by the estates of the duchy (early parliamentarism).
Split into simpler sentences: Because he had no sons, he has concluded the Treaty of Kępno in 1282, making duke Przemysł II his successor in all his possessions. The treaty was confirmed by the estates of the duchy (early parliamentarism).