Complex sentence: The chain of events forced the last emperor of China, Puyi, to abdicate, on February 12 upon Yuan Shikai's suggestion to Empress Dowager Longyu, who signed the abdication papers.
Split into simpler sentences: The chain of events forced the last emperor of China, Puyi, to abdicate on February 12. He did so upon Yuan Shikai's suggestion to Empress Dowager Longyu, who also signed the abdication papers.