“On all important occasions… the opportunists come forward with an ultimatum, which they carry out with the aid of their numerous connections with the bourgeoisie, of their majority on the executives of the trade unions, etc. Unity with the opportunists actually means today, subordinating the working class to “its” national bourgeoisie, alliance with it for the purpose of oppressing other nations and of fighting for great-power privileges, it means splitting the revolutionary proletariat in all countries.”
Vladimir Lenin, Socialism and War