Complex sentence: After the primary empress Danashri was overthrown in 1340 because of the rebellion by his brother Tanggisi, Toghun Temür try to install Öljei Khutugh as an empress, Bayan, who held real power, opposed it.
Split into simpler sentences: After the primary empress Danashri was overthrown in 1340 because of the rebellion by her brother Tanggisi, Toghun Temür tried to install Öljei Khutugh as the empress. However Bayan, who held real power, opposed it.