 Zhou's most lucrative business was generated by several opium plantations that Zhou established in remote areas.Although the CCP had been engaged in the eradication of opium smoking since its establishment, Zhou justified opium production and distribution in KMT-controlled areas by the huge profits generated for the CCP, and by the debilitating effects that opium addiction might have on KMT soldiers and government officials.In 1943, Zhou's relationship with Chiang Kai-shek deteriorated, and he returned permanently to Yan'an.