The "Manifesto" is the most influential of all Socialist documents. It is at once a firebrand and a formulary. Its formulæ are the well-known Marxian principles; its energy is the youthful vigor and zeal of ardent revolutionists. Nearly all the generalizations of _Capital_ are found in the "Manifesto." This is important, for it gave the sanction of a social theory to the Socialist movement. Hitherto there had been only utopian generalizations and keen denunciations of the existing order. It was of the greatest importance that early in the development of the movement it was given an economic theory expressed in such lucid terms, with the gusto of youth, and in the terminology of science, that it remains to-day the best synopsis of Marx's "Scientific Socialism." As a piece of campaign literature it is unexcelled. Combined with its clearness of statement, its economic reasoning, its terrific arraignment of modern industrial society, there is a lofty zeal and power that placed it in the front rank of propagandist literature. Engels, the surviving partner of the Marxian movement, wrote in the preface of the edition of 1888: "The 'Manifesto' being our joint production, I consider myself bound to say that the fundamental proposition which forms its nucleus belongs to Marx." That proposition embraced the materialistic theory of social evolution, that "the whole history of mankind has been a history of class struggles ... in which nowadays a stage has been reached where the exploited and oppressed classes--the proletariat--cannot attain their emancipation from the sway of the exploiting and ruling classes--the bourgeoisie--without at the same time and once for all emancipating society at large from all exploitation, oppression, class distinctions, and class struggles." This liberation was, of course, to be accomplished by revolution. The "Manifesto" closes with these spirited and oft-quoted words: "The communists disdain to conceal their views and aims. They openly declare that their ends can be obtained only by the forcible overthrow of all existing social conditions. Let the ruling class tremble at a communist revolution. The proletarians have nothing to lose but their chains, they have a world to win. Workingmen of all countries, unite." This was the language and the spirit of the times. The "Manifesto" was published only a few days before the February revolution of 1848. For a moment the ruling class did tremble; but the ill-timed uprisings were promptly suppressed and the days of reaction set in. Soon the workingmen of different countries were busy with the stupendous development of industry which followed in the wake of the wars and revolutions that had harassed the Continent for over fifty years. The revival of industry brought a renewal of international trade. This was followed by a wider exchange of views and greater international intimacy. In 1862 the first International Exposition was held.