 Chiang was somewhat aware of these activities and introduced efforts to suppress them, but was generally unsuccessful.In July 1939, while in Yan'an to attend a series of Politburo meetings, Zhou had an accident horseback riding in which he fell and fractured his right elbow.Because there was little medical care available in Yan'an, Zhou traveled to Moscow for medical treatment, using the occasion to brief the Comintern on the status of the united front.