On April 12, 1927, brutal attacks on Communist unions in Shanghai by Kuomintang troops and affiliated underground gangs brought the first united front between the Nationalists and the Chinese Communists to a bloody conclusion. More than just a political defeat for the Communists, the purge necessitated a change in revolutionary strategy by indicating the frailty of Communist organization in the urban areas. The cities, as bastions of Chinese and foreign wealth and power, did not offer a safe haven for labor unions, regardless of Marxian dictates which required the proletariat to serve as engine of the future revolution.