In 1868, Dana set up a rival newspaper, the "New York Sun", at which he was editor-in-chief. In April 1857, Dana invited Marx to contribute articles, mainly on military history, to the "New American Cyclopedia", an idea of George Ripley, Dana's friend and literary editor of the "Tribune". In all, 67 Marx-Engels articles were published, of which 51 were written by Engels, although Marx did some research for them in the British Museum. By the late 1850s, American popular interest in European affairs waned and Marx's articles turned to topics such as the "slavery crisis" and the outbreak of the American Civil War in 1861 in the "War Between the States". Between December 1851 and March 1852, Marx worked on his theoretical work about the French Revolution of 1848, titled "The Eighteenth Brumaire of Louis Napoleon". In this he explored concepts in historical materialism, class struggle, dictatorship of the proletariat, and victory of the proletariat over the bourgeois state.