Complex sentence: In the early 19th century, Britain's victory over Qing China in the First Opium War forced China to sign an unequal treaty, this marked the beginning of the end for the "tianxia" concept.
Split into simpler sentences: In the early 19th century, Britain's victory over Qing China in the First Opium War forced China to sign an unequal treaty. This marked the beginning of the end for the "tianxia" concept.