In 1152 King Conrad III died and was succeeded by his nephew Frederick Barbarossa. With the accession of this energetic ruler, the hopes of Agnes and Władysław II of returning to Poland were rekindled. With the encouragement of his aunt, the new German king launched an expedition against Poland in 1157. The campaign was a success but unexpectedly Barbarossa did not restore Władysław II to the Polish throne. Instead High Duke Bolesław IV was declared a vassal of Emperor Frederick and was compelled to pay tribute to him. In compensation to Władysław II, he forced Bolesław to promise the restitution of the Silesian duchy to Władysław's sons.