[2] He suffered multiple gunshot wounds, as well as contracting gangrene in the front-line trenches of the battle of the Somme, requiring amputation of both feet to the instep.

[3] Campbell and his close associate Willie Gallacher were joint secretaries of the British Bureau of the Red International of Labour Unions, with Tom Mann chairman of the organisation.

On 25 July 1924, Campbell published an article entitled "An Open Letter to Fighting Forces", which called on the armed forces to unite to form "the nucleus of an organisation that will prepare the whole of the soldiers, sailors and airmen, not merely to refuse to go to war, or to refuse to shoot strikers during industrial conflicts, but will make it possible for the workers, peasants and soldiers and airmen to go forward in a common attack upon the capitalists and smash capitalism for ever, and institute the reign of the whole working class.

This became known as the "Campbell Case", and when the first Labour government dropped the prosecution, the combined Conservative and Liberal Party opposition won a vote of no confidence, which in turn led to the 1924 general election.

On the question of empire, we advocated that the Labour movement should force the government to abandon the brutal and cowardly repression of the struggling colonial peoples.

[7] Campbell was elected to the Executive Committee of the Communist International in 1928, and used the opportunity to argue against its hostility to joint work with the Labour Party.

[7] On 3 September 1939, Prime Minister Neville Chamberlain spoke to the nation on the BBC, announcing the declaration of war between Britain and Nazi Germany.

[9] However, backed with the knowledge of the details of the Molotov–Ribbentrop Pact and seeking to preserve the Soviet Union by turning Hitler's attention to Western Europe, the Comintern quickly signalled that the conflict was to be portrayed by the world communist movement as an "Imperialist War" between two more or less equally culpable blocs of capitalist nations.

On 2 and 3 October the governing Central Committee of the CPGB met and voted 21–3 in favour of the Communist International's "Imperialist War" thesis.