Central and peripheral location presuppose and supplement one another. One people inhabits the interior of an island or continent whose rim is occupied by another. The first suffers from exclusion from the sea and therefore strives to get a strip of coast. The coast people feel the drawback of their narrow foothold upon the land, want a broader base in order to exploit fully the advantages of their maritime location, fear the pressure of their hinterland when the great forces there imprisoned shall begin to move; so they tend to expand inland to strengthen themselves and weaken the neighbor in their rear. The English colonies of America, prior to 1763, held a long cordon of coast, hemmed in between the Appalachian Mountains and the sea. Despite threats of French encroachments from the interior, they expanded from this narrow peripheral base into the heart of the continent, and after the Revolution reached the Mississippi River and the northern boundary of the Spanish Floridas. They now held a central location in relation to the long Spanish periphery of the Gulf of Mexico. True to the instincts of that location, they began to throw the weight of their vast hinterland against the weak coastal barrier. This gave way, either to forcible appropriation of territory or diplomacy or war, till the United States had incorporated in her own territory the peripheral lands of the Gulf from Florida Strait to the Rio Grande. [See map page 156.] [Sidenote: Russian expansion in Asia.] In Asia this same process has been perennial and on a far greater scale. The big arid core of that continent, containing many million square miles, has been charged with an expansive force. From the appearance of the Aryans in the Indus Valley and the Scythians on the borders of Macedonia, it has sent out hordes to overwhelm the peripheral lands from the Yellow Sea to the Black, and from the Indian Ocean to the White Sea.[251] To-day Russia is making history there on the pattern set by geographic conditions. From her most southerly province in Trans-Caspia, conquered a short twenty-five years ago, she is heading towards the Indian Ocean. The Anglo-Russian convention of August 31st, 1907, yielding to Russia all northern Persia as her sphere of influence, enables her to advance half way to the Persian Gulf, though British statesmen regard it as a check upon her ambition, because England has secured right to the littoral. But Russia by this great stride toward her goal is working with causes, satisfied to let the effects follow at their leisure. She has gained the best portion of Persia, comprising the six largest cities and the most important lines of communication radiating from the capital.[252] This country will make a solid base for her further advance to the Persian Gulf; and, when developed by Russian enterprise in railroad building and commerce, it will make a heavy weight bearing down upon the coast. The Muscovite area which is pressing