2. Capitalism was no longer supreme as it had been before 1900. On the contrary, since 1950 the planet has been divided along class lines--capitalism versus socialism. 3. Socialism-communism is one of the most obvious facts of present-day planetary life. 4. Capitalism is losing ground, especially in Europe. 5. Socialism is gaining ground, especially in Eurasia. Co-existence presupposes recognition of these five propositions and a willingness to abide by the outcome of the evolutionary-revolutionary process, through which the western world is passing. During several centuries, ending in 1900, western civilization passed through an era of consolidation and integration that brought its sovereign segments into increasing stable relationships. The most advanced of these relationships took political shape in the half-dozen European empires which controlled the planet in 1900. Side by side with the consolidation of the planet into nations and empires there was another process, world-wide in scope, which made the facts and products of science and technology and their duplication the common property of mankind, creating a cultural synthesis far more universal than the political synthesis in nations, empires, the League of Nations or the United Nations. Any social synthesis includes positive and negative aspects which function side by side. One builds up. The other wears down. For centuries the building forces in western civilization were in the ascendant. Since the turn of the century a shift of forces has been under way. The wearing down forces presently are in the ascendant. Had it been less competitive and more cooperative and co-ordinated, western civilization might have taken another step in advance by extending cultural unification into the political arena. The League of Nations and the United Nations were efforts in this direction. Neither succeeded in breaking down sovereignty far enough to permit planet-wide political federation. Having failed to co-ordinate and establish a planet-wide authority during the critical years following 1870, western civilization accepted the antithesis of co-ordination and entered a period of fragmentation: 1. During the century and a half from 1815 to the present day, as facilities for co-ordination were multiplied by discovery and invention, Europe remained stubbornly fragmented into more than a score of sovereign states. Minor changes were made in boundary lines and in internal relationships of property and privilege, but the European maps of the period present a record of persistent fragmentation of the continent into strongly frontiered sovereign segments. 2. Break-up of the European empires after two general wars led to the fragmentation of each empire into self-determining sovereign units.