When imperialism launches a war of aggression against such a country, all its various classes, except for some traitors, can temporarily unite in a national war against imperialism. At such a time, the contradiction between imperialism and the country concerned becomes the principal contradiction, while all the contradictions among the various classes within the country (including what was the principal contradiction, between the feudal system and the great masses of the people) are temporarily relegated to a secondary and subordinate position. So it was in China in the Opium War of 1840, the Sino-Japanese War of 1894 and the Yi Ho Tuan War of 1900, and so it is now in the present Sino-Japanese War.

But in another situation, the contradictions change position. When imperialism carries on its oppression not by war, but by milder means–political, economic and cultural–the ruling classes in semi-colonial countries capitulate to imperialism, and the two form an alliance for the joint oppression of the masses of the people. At such a time, the masses often resort to civil war against the alliance of imperialism and the feudal classes, while imperialism often employs indirect methods rather than direct action in helping the reactionaries in the semi-colonial countries to oppress the people, and thus the internal contradictions become particularly sharp. This is what happened in China in the Revolutionary War of 1911, the Revolutionary War of 1924-27, and the ten years of Agrarian Revolutionary War after 1997. Wars among the various reactionary ruling groups in the semi-colonial countries, e.g., the wars among the warlords in China, fall into the same category.

When a revolutionary civil war develops to the point of threatening the very existence of imperialism and its running dogs, the domestic reactionaries, imperialism often adopts other methods in order to maintain its rule; it either tries to split the revolutionary front from within or sends armed forces to help the domestic reactionaries directly. At such a time, foreign imperialism and domestic reaction stand quite openly at one pole while the masses of the people stand at the other pole, thus forming the principal contradiction which determines or influences the development of the other contradictions. The assistance given by various capitalist countries to the Russian reactionaries after the October Revolution is an example of armed intervention. Chiang Kai-shek's betrayal in 1927 is an example of splitting the revolutionary front.