Defensism
Invocation of the "right to national defense" to support the recruitment and slaughter of workers in defense of one national state - or aspiring state - against another.
Origins
The 1914 war, the first imperialist world war, marks a point of no return in the development of imperialism as a trend. Every national capital sells war as the ultimate solution to the pending tasks of the bourgeois revolution of the previous century. Germany takes up the banner of putting an end to tsarism, the last bastion of feudal reaction in Europe, France and Britain claim to represent democracy against the barbaric Prussian system and together with the US will defend self-determination as a form of the pending national liberation in Central and Eastern Europe. War is shamelessly labelled as the war to end all wars.
But the reality is that the giant organization of capitalist production has become a machine of annihilation. Millions of workers are being killed en masse in the battlefields of Europe in a war organized in the Taylorist way, at the stroke of a battle plan and a chronometer. The defensive discourse, the invocation of the right to national defense against a foreign invasion is the ultimate imperialist argument: every bourgeoisie defending itself against its neighbors means nothing but a total carnage.
The main figures of the Second International and the leadership of its parties and unions will turn defensism, once the war has begun, into a way of encouraging the workers to continue sacrificing themselves en masse and killing each other until "a democratic peace without annexations or compensation" is achieved.
Marxist criticism
Inevitably, the invocation of the "right to national defense" will go hand in hand with a whole bunch of leaf litter vindicating a non-existent "International Law" and endless discussions about who is the "aggressor" or the "guilty one". But...
Whatever the truth about the direct responsibility for the outbreak of war, one thing is certain: the war resulting in this chaos is the result of imperialism, of the attempt by the capitalist classes in every country to satisfy their greed for profit through the exploitation of human labor and the natural resources of the entire world.
Zimmerwald Manifesto against the war. LD Trotsky, 1915
Or in Rosa Luxemburg's words:
In the discussion about the general causes of war and their significance, it is not a question of solving the problem of who is "guilty". Germany certainly does not have the slightest right to speak of a war of defense, but France and England have no greater justification. Nor do they protect their national existence, but their world political existence, their old colonial possessions, from the attacks of the German upstart.
Rosa Luxemburg. The Crisis of Social Democracy (Junius pamphlet), 1916
Rosa Luxemburg's basic argument is that imperialism is a stage of capitalism as a whole. Even if, for some time, some countries might have been relatively left out, the entry into a stage of world wars would express by itself the impossibility of a development of national capital independent of the conditions of imperialism during the new phase of decadence in which the system was immersed.
If the term "national" remained, its actual content and function have become its opposite; it acts only as a miserable cover for imperialist aspirations and a battle cry for their rivalries, as the only and last ideological means for achieving the adherence of the masses of people and playing their role as cannon fodder in the imperialist wars.
Rosa Luxemburg. The Crisis of Social Democracy, 1916
As she insisted in another pamphlet later that year:
In this age of unbridled imperialism, there can be no more national wars. National interests serve only as a pretext to put the masses of people in the service of their mortal enemy: imperialism.
Rosa Luxemburg. The Tasks of Social Democracy, 1916
Not only is there no possibility of nations or national liberations with a progressive sense in the decadence in which capitalism entered through the door of world wars, only revolutionary defeatism can effectively confront wars and the existence of a permanent tendency towards militarism and warlike conflicts.
The result of the great war is that it is impossible for the capitalist classes to get out of their difficulties as long as they remain in power. We now understand the truth contained in the phrase first formulated by Marx and Engels as the scientific basis of socialism, in the great letter of our movement, the Communist Manifesto. Socialism, they said, will become a historical necessity.
Speech at the Founding Congress of the Communist Party in Germany Rosa Luxemburg, 1919
And revolutionary defeatism means nothing other than turning imperialist war into class war.
http://dictionary.marxismo.school/DefensismIn order to fool the proletariat and distract its attention from the only truly emancipatory war, that is, the civil war against the bourgeoisie, both in its "own" country and in that of "others", the bourgeoisie of each country makes an effort, with misleading phrases about patriotism, to extol the meaning of "their" national war and to ensure that it aims at defeating the adversary not for the sake of plundering and territorial conquests, but for the sake of "emancipating" all other peoples except their own. (…)
The transformation of the present imperialist war into a civil war is the only just proletarian slogan, indicated by the experience of the Commune, pointed out by the Basel resolution (1912) and derived from all the conditions of the imperialist war among the highly developed bourgeois countries. However great the difficulties of such a transformation may seem at one time or another, socialists will never give up systematic, persevering and continuous preparatory work in this direction, since war is a fact.
Only by following this path can the proletariat free itself from its dependence on the chauvinist bourgeoisie and take, in one form or another and with greater or lesser speed, the decisive steps toward the true freedom of the people and toward socialism.
"The War and the Social Democracy of Russia. Lenin, 1914