Too weak to resist Japan, China appealed to the League of Nations for help. Japan withdrew from the League of Nations after being condemned for its incursion into Manchuria. The two nations then fought several battles, in Shanghai , Rehe and Hebei , until the Tanggu Truce was signed in 1933. Thereafter, Chinese volunteer forces continued the resistance to Japanese aggression in Manchuria , and Chahar and Suiyuan .  After the 1936 Xi'an Incident , the Kuomintang and communist forces agreed on a ceasefire to present a united front to oppose Japan.