Complex sentence: Chifeng was established the third largest city of Rehe Province after Chengde and Chaoyang, After the Operation August Storm, the Soviet-Mongolian Cavalry-Mechanized Group had entered Chifeng.
Split into simpler sentences: Chifeng was established as the third largest city of Rehe Province after Chengde and Chaoyang. After Operation August Storm, the Soviet-Mongolian Cavalry-Mechanized Group entered Chifeng.