This is a stirring decade, and it completely changed the territorial status of the United States. By 1819 the Atlantic coast all belonged to the United States, from the St. Croix River around Florida to the Sabine; the country was reaching out toward Mexico, and was building a bridge of solid territory across the continent, where, as all the world knew, far to the south of Oregon lay the harbor of San Francisco, the best haven on the Pacific coast. The bold conceptions of Jefferson and John Quincy Adams and their compeers included the commercial and political advantages of a Pacific front; and they were consciously preparing the way for the homes of unborn generations under the American flag. One result of the new position of the United States was to bring out sharply a territorial rivalry with Great Britain. The War of 1812 had been an attempt to annex Canada, and after it was over a controversy as to the boundary between Maine and Nova Scotia kept the two countries harassed until its settlement in 1842.[11] After that the rivalry for Oregon, which had been held in joint occupation since 1818, was intensified. About 1832 immigration began in which the Americans outran the English; and it was fortunate for both countries that in 1846 the disputed territory was divided by a fair compromise line, the forty-ninth parallel.[12] A third territorial controversy was fought out within the limits of the Union itself, between the friends and opponents of the annexation of Texas, in 1845.[13] This was the first instance of an American colony planting itself within the acknowledged limits of another power, until it was strong enough to set up for itself as an independent state and to ask for admission to the Union. The annexation of Texas inevitably led to a movement on California, which could be obtained only by aggressive war upon Mexico, and for connection with which the possession of New Mexico was also thought necessary. Ever since 1820 explorers had been opening up the region between the Mississippi and the Pacific,[14] and it was known that there were several practicable roads to that distant coast.[15] The annexation of California almost led the United States into a serious territorial adventure; for apparently nothing but the hasty treaty negotiated by Trist in 1848 stopped a movement for the annexation of the whole of Mexico.[16] The Gadsden Purchase of 1853 conveniently rounded out the cession of New Mexico and closed this second era of territorial expansion.