Plekhanov and Struve were at that time the chief exponents of Marxism: they adopted the teaching of Karl Marx as regards the necessary sequence of economic stages - feudalism, bourgeois individualism, capitalism, proletarian upheaval.
Though I think Karl Marx overestimated its importance when he identified this conflict as the fundamental struggle of history, it certainly has been a constant.
Studying the writings of Karl Marx he became a convert to an extreme revolutionary, socialistic and atheistic creed; but though he entered into correspondence with Marx, with the object of starting a revolutionary movement, he does not appear to have taken any overt part in the events of 1848-1849.
In Paris Ruge tried to act with Karl Marx as co-editor of the Deutsch-Franzosische JahrNicher, but had little sympathy with Marx's socialistic theories, and soon left him.
With Liebknecht he belonged to the branch of the socialists which was in close correspondence with Karl Marx and the International, and refused to accept the leadership of Schweitzer, who had attempted to carry on the work after Lassalle's death.