In addition to the aggressive neighbor, there is often a more sustained force that may draw the activities of a people toward one or another boundary of their territory. This may be the abundance of land and unexploited resources lying on a colonial frontier and attracting the unemployed energies of the people, such as existed till recently in the United States,[257] and such as is now transferring the most active scenes of Russian history to far-away Siberia. But a stronger attraction is that of a higher civilization and dominant economic interests. So long as the known world was confined to the temperate regions of Europe, Asia and Africa, together with the tropical districts of the Indian Ocean, the necessities of trade between Orient and Occident and the historical prestige of the lands bordering on the Mediterranean placed in this basin the center of gravity of the cultural, commercial and political life of Europe. The continent was dominated by its Asiatic corner; its every country took on an historical significance proportionate to its proximity and accessibility to this center. The Papacy was a Mediterranean power. The Crusades were Mediterranean wars. Athens, Rome, Constantinople, Venice, and Genoa held in turn the focal positions in this Asiatic-European sea; they were on the sunny side of the continent, while Portugal and England lay in shadow. Only that portion of Britain facing France felt the cultural influences of the southern lands. The estuaries of the Mersey and Clyde were marshy solitudes, echoing to the cry of the bittern and the ripple of Celtic fishing-boat. [Sidenote: Change of historical front.] After the year 1492 inaugurated the Atlantic period of history, the western front of Europe superseded the Mediterranean side in the historical leadership of the continent. The Breton coast of France waked up, the southern seaboard dozed. The old centers in the Aegean and Adriatic became drowsy corners. The busy traffic of the Mediterranean was transferred to the open ocean, where, from Trafalger to Norway, the western states of Europe held the choice location on the world's new highway. Liverpool, Plymouth, Glasgow, Hamburg, Rotterdam, Antwerp, Cherbourg, Lisbon and Cadiz were shifted from shadowy margin to illuminated center, and became the foci of the new activity. Theirs was a new continental location, maintaining relations of trade and colonization with two hemispheres. Their neighbors were now found on the Atlantic shores of the Americas and the peripheral lands of Asia. These cities became the exponents of the intensity with which their respective states exploited the natural advantages of this location.