Pacifism, the preaching of peace in the abstract, is one of the means of duping the working class. Under capitalism, particularly in its imperialist stage, wars are inevitable. On the other hand, however, Social-Democrats cannot over look the positive significance of revolutionary wars, i.e., not imperialist wars, but such as were fought, for instance, between 1789 and 1871, with the aim of doing away with national oppression, and creating national capitalist states out of the feudal decentralised states, or such wars that may be waged to defend the conquests of the proletariat victorious in its struggle against the bourgeoisie.

At the present time, the propaganda of peace unaccompanied by a call for revolutionary mass action can only sow illusions and demoralise the proletariat, for it makes the proletariat believe that the bourgeoisie is humane, and turns it into a plaything in the hands of the secret diplomacy of the belligerent countries. In particular, the idea of a so-called democratic peace being possible without a series of revolutions is profoundly erroneous.

https://www.marxists.org/archive/lenin/works/1915/feb/19.htm