A pause in advance followed, until events showed that Isthmian control was a national necessity to the United States. It suffices here to note the conclusion of a long diplomatic history. In 1903 the United States, having failed to obtain concessions of the desired kind from Colombia, supported the province of Panamá in her secession from Colombia, and speedily obtained from the newly formed republic a perpetual lease of the canal zone, together with a practical protectorate over the Republic of Panamá. The United States then proceeded to construct and fortify the canal. She also procured from Nicaragua exclusive rights concerning the construction of any canal through Nicaraguan territory, and erected in fact a kind of protectorate over that republic. Meanwhile, in the Antilles events were shaping towards control from the north. A long-standing trouble concerning Cuba culminated in the Spanish-American War of 1898, which brought about the annexation of Porto Rico and the Philippines to the United States, while Cuba became a republic under the tutelage of that Power. Five years later the United States, in order to save the Dominican Republic from European pressure, undertook the administration of the revenues of that state. In 1915 she interposed to suppress a revolution in Haiti. Finally last year (1917) she purchased from Denmark the islands of St Thomas and Santa Cruz. Recent rumours as to a proposed further purchase--that of Dutch Guiana--have been officially denied. These advances have not gone beyond the Caribbean area, where geographical conditions place the United States in a dominant position. Her relations with the more distant southern countries, not touching the Mediterranean Sea of the New World, fall into a different category and do not directly concern the immediate topic. But in the Caribbean area the United States has established a Sphere of Influence, not indeed explicitly defined as such, but recognised in effect by other governments and accepted by some at least of the republics occupying that region. The events of the last twenty years further indicate that the United States is undertaking the obligation, usual in such cases, of imposing a "Pax Americana." As in similar instances elsewhere, this Pax Americana has not quite clearly marked its geographical limit, nor is it guided by any theoretical consistency, but rather by the merits of the case and the test of immediate expediency in each instance. Thus, whereas the United States enforces peace in Haiti and definitely undertakes to maintain internal tranquillity in Cuba, she has on the other hand withdrawn from interposition in Mexico. The outside world has, on the whole, treated these matters as the concern of the United States and respected the working of the Pax Americana. Meanwhile, geographical proximity has favoured North American commerce, and in recent years more than half the trade of Central America was carried on with the United States.