The existence of a labour aristocracy is explained by the super-profits of monopoly, which allows the capitalists to devote a part (and not a small one at that!) to bribe their own workers, to create something like an alliance between the workers of a given nation and their capitalists against the other countries. This "bribery" operates through trusts, the financial oligarchy, high prices, etc. (i.e. something like joint monopolies between a given capitalism and its workers).