The question of sovereignty was not left to Great Britain and the United States alone, on the withdrawal of Spain. More than two decades before, Russia had entered this region with an assertion of her right to make settlement on unoccupied territory, and recently had grown somewhat imperious in the tone of her assertion of that right. This intrusion of Russia followed close upon the Nootka Convention, and was the logical consequence of the principle for which Great Britain had secured recognition in that convention. It will be remembered that Great Britain did not base her right to make, and to have restored to her, the Nootka settlement so much on priority in discovery of the region in which the settlement was made, as on the broader principle of her right to settle in any place by whomsoever discovered, which after a reasonable time she might find unoccupied. This principle could not be valid for England alone, and Russia was not long in discovering its wider validity. After England's previous assertion of this principle, in the affair of the Falkland Islands, Spain had taken alarm, and had sent explorers along the Northwest Coast with the intention of making good her claim to it by the northward extension of her settlements. In like manner Russia now began to extend her claim into new territory by availing herself of this same principle. The grant of Emperor Paul I to the Russian American Company in 1799 gave the company exclusive possession from latitude 55° northward to the Arctic Sea, with the right to extend their settlements south of 55°, if they did not thereby encroach on territories occupied by other powers. In the spring of 1808 the Russian government opened a correspondence with the government of the United States in relation to what Russia was pleased to term the illicit traffic of American traders with the natives inhabiting Russian territories. It appeared in the course of this correspondence that Russia claimed the coast at this time as far south as the Columbia River. The right to make settlements, or at least to establish trading posts, it seems she did not confine to this southern limit, for in 1816, a Russian trading post was established as far south as latitude 38°, in Northern California. In this later and more aggressive policy of extending her claims southward, Russia is thought to have been influenced by the publication in Paris in 1808 of Humboldt's Political Essay on New Spain, in which such a destiny for Russia had been hinted at. However this may have been, it is certain that the accounts of Humboldt's travels were eagerly read by the Russian Emperor, and an increased boldness and aggressiveness are observable in Russian policy after the publication of this work.