Complex sentence: When An Lushan submitted a petition to have 32 non-Han generals under him replace Han generals, Emperor Xuanzong immediately agreed, despite stern arguments from Yang Guozhong and his fellow chancellor Wei Jiansu that this was a sign of impending rebellion.
Split into simpler sentences: When An Lushan submitted a petition to have 32 non-Han generals under him replace Han generals. This was accepted by Emperor Xuanzong, despite opposition from Yang Guozhong and his fellow chancellor Wei Jiansu who took An's use of non-Han generals as a sign of impending rebellion.