At the forty-second parallel, the southern boundary of Oregon country and the northern boundary claimed by Spain and later Mexico became a dividing line in competing claims to the Oregon territory by Spain, Great Britain, Russia, the United States, and Mexico. Spain based its claim on Vasco Nunez de Balboa's first sight of the Pacific Ocean in 1513 and controlled the entire Pacific coast until the Nootka Treaties of 1790, 1793, and 1794; in 1819, Spain and the United States agreed to a forty-second parallel boundary. Great Britain based its claim on Drake's 1578 voyage, the voyages of Cook and Vancouver, and MacKenzie's overland trip to the Pacific; after blunting Spain's claims at Nootka Sound, Britain jointly occupied the region from the forty-second parallel to fifty-four degrees forty minutes latitude with the U.S. beginning in 1818, and the treaty of June 15, 1846 set the boundary at the forty-ninth parallel. Russia sought in 1821 to extend the Russian-American Company's influence from Alaska to San Francisco by ukase, but President James Monroe answered with the Monroe Doctrine on December 2, 1823, and the treaty of 1824 set the U.S.-Russian boundary at fifty-four degrees forty minutes north latitude. The United States grounded its claim in Gray's 1792 discovery of the Columbia River and in the Lewis and Clark expedition, and by 1846 American immigration had surpassed British influence; Texas entered the Union on December 29, 1845 as the twenty-eighth state, and Iowa on December 28, 1846. Mexico inherited Spain's lands south of this line after the revolution of 1821, and by 1823 the Republic of Mexico had been confirmed; Augustin de Iturbide, its most active proponent, was executed by loyalists, and by February 2, 1848 more than five hundred thousand square miles of Mexico had become the American Southwest.