The struggle to uproot capitalism and plant the seeds of socialism has always been an international task. It is not out of sentimentality that Marx and Engels proclaimed “Workers of the world unite!” Capitalism is an international economic system and therefore the struggle against it must be international. While for all practical purposes, the workers must organize themselves at home as a class with their country as their immediate arena of struggle, the real ultimate context of the class struggle is international.
The history of the Fourth International was one of a struggle to keep the genuine international spirit of the working class struggle alive when Stalin and his bureaucratic clique were undermining it. While Stalin was preparing to dismantle the Third International and renouncing the struggle for world socialism, Leon Trotsky was building, under a very difficult situation, the Fourth International not only to defend the first proletarian revolution, the October Revolution, but also to spread it beyond its border.
The building of the Fourth International was also part of Trotsky’s effort to recruit and educate a new generation of genuine Bolsheviks who would be able to finish what the Russian Bolsheviks had started. What is important is not the apparatus but the ideas that the Fourth International sought to protect and pass on to the next generation.
— From Keeping the International alive: a history of the Fourth International