Complex sentence: A major plague pandemic in historic times, called the Third Pandemic, began in China in 1855, spreading the bubonic plague to all inhabited continents, and ultimately killed more than 12 million people in India and China alone.
Split into simpler sentences: A major plague pandemic in historic times, called the Third Pandemic, began in China in 1855. The bubonic plague spread to all inhabited continents, and ultimately killed more than 12 million people in India and China alone.