Does not the present war also teach us that everything that is immature or decaying, everything that is conventional or diplomatic, will collapse at the first blow?

V. I. Lenin
The Question of the Unity of Internationalists

There is and there can be no other way of testing the real might of a capitalist state than by war. War does not contradict the fundamentals of private property—on the contrary, it is a direct and inevitable outcome of those fundamentals. Under capitalism the smooth economic growth of individual enterprises or individual states is impossible. Under capitalism, there are no other means of restoring the periodically disturbed equilibrium than crises in industry and wars in politics.

V. I. Lenin
On the Slogan for a United States of Europe

she looks about her and finds her children crying for bread. She is desperate, but she must not appeal or complain to any one. She must hold her tongue and suffer inwardly. But how can she silence her children? She must not even share the sympathy of her husband at the front, because that cripples her soldier husband's fighting powers. Her soldier husband must `hold on' and 'steal' in the land of her neighbors. He must hold on and 'suffer' because the capitalists, the hurrah patriots and the armor-plate kings have willed it so. Every one must keep his or her tongue between the teeth, for the war profiteers must make money out of the want and misery of the wives and their husband soldiers at the front.

Karl Liebknecht
The Future Belongs to the People

Thus wars are rooted in the very essence of capitalism; they will end only when the capitalist system ceases to exist, or when the immensity of human and financial sacrifice caused by the development of military technique, and the indignation which armaments arouse in the people, lead to the elimination of the system.

V. I. Lenin

"The history of all hitherto existing society is the history of class struggles.

Freeman and slave, patrician and plebeian, lord and serf, guild-master and journeyman, in a word, oppressor and oppressed, stood in constant opposition to one another, carried on an uninterrupted, now hidden, now open fight, a fight that each time ended, either in a revolutionary reconstitution of society at large, or in the common ruin of the contending classes."

The revolution here is neither abstract nor rhetorical; it burns, it sweats, it shovels. The train moves because workers move it. History accelerates because labor fuels it.

every class which is struggling for mastery, even when its domination, as is the case with the proletariat, postulates the abolition of the old form of society in its entirety and of domination itself, must first conquer for itself political power in order to represent its interest in turn as the general interest, which in the first moment it is forced to do.

Karl Marx. The German Ideology. 1845

Wars and all their calamities are produced by capitalism, which keeps millions of working people in bondage, sharpens the struggle between nations, and turns the slaves of capital into cannon fodder. A world-wide socialist army of the revolutionary proletariat is alone capable of putting an end to this oppression and enslavement of the masses and to these massacres of slaves in the interests of the slave-owners.

V. I. Lenin
To All the Citizens of Russia

We say: our aim is to achieve a socialist system of society, which, by eliminating the division of mankind into classes, by eliminating all exploitation of man by man and nation by nation, will inevitably eliminate the very possibility of war.

Lenin
War and Revolution (1917)