Complex sentence: During the Warlord Era in the early twentieth century, Liaoning was under the Fengtian Clique, including Zhang Zuolin and his son Zhang Xueliang; in 1931, Japan invaded and the area came under the rule of the Japanese-controlled puppet state of Manchukuo.
Split into simpler sentences: During the Warlord Era in the early twentieth century, Liaoning was under the Fengtian Clique, including Zhang Zuolin and his son Zhang Xueliang. In 1931, Japan invaded and the area came under the rule of the Japanese-controlled puppet state of Manchukuo.