After the 1937 Marco Polo Bridge Incident, China and Japan formally went to war. When the Kuomintang and communists declared a united front to fight the Japanese, Peng was confirmed as a general in the unified command structure of the NRA. At the August 20, 1937 Luochuan Conference (), Mao believed that the united front should be used as a feint by giving token resistance to the Japanese but saving the strength of the Red Army for the eventual confrontation with the Kuomintang. However, Peng, along with most other senior military and political leaders, disagreed and believed that the Red Army should genuinely focus on fighting the Japanese. Mao was not able to force his position, and the communists co-operated with the Kuomintang and fought the Japanese.