A highly important letter calling for solidarity following the full scale Japanese invasion of China and signed by Mao Zedong and Zhu De is sure to be on the radar of China’s passion investors when it comes to auction in London on December 15th.

The letter has a reserve price of £100,000 - £150,000 but given the uniqueness and significant historical context the hammer price could far exceed this.

This letter, written by the Communist Party leader and then guerrilla leader who would become one of the most significant historical figures of the century, whose actions and decisions would impact upon hundreds of millions of lives, was written to the British politician Clement Attlee (1883-1967), then leader of the Labour Party.

This attempt to elicit British support against Japan is an extraordinarily early instance of Mao engaging in international diplomacy and is an exceptionally rare example of Mao’s signature. Only one letter signed by Mao has been sold at auction on the international auction market in recent decades.

The context of this letter was the full-scale invasion of China initiated by Japan on 7 July 1937 after many years of aggressive expansion. Faced with this existential threat, the Communists united with their Nationalist enemies to form the Second United Front.

The Red Army was incorporated, at least in name, into the Nationalist military structure as the New Fourth Army and the Eighth Route Army. The latter was commanded by Zhu De (1886-1976), one of the principal founders of the People’s Liberation Army, who also signed the current letter.

The Communists had reached Yan'an in north-west China at the end of the Long March in December 1936, and it now became the centre of their resistance to the Japanese. It was to be a campaign characterised by guerrilla warfare, although they won a morale-boosting victory in a set-piece battle at Pingxingguan on 25 September 1937.