Complex sentence: He also entered into an alliance with Bernhard II of Rohr, Archbishop of Salzburg, who allowed him to took possession of the fortresses of the Archbishopric in Carinthia, Carniola and Styria.
Split into simpler sentences: He also entered into an alliance with Bernhard II of Rohr, Archbishop of Salzburg. The Archbishop even allowed him to took possession of the fortresses of the Archbishopric in Carinthia, Carniola and Styria.