<Tr> <Th> July 5, 1843 </Th> <Td> Local settlers created a provisional government for Oregon Country . While not official, it did maintain some jurisdiction over the area . </Td> <Td> Unofficial change: Northwestern North America: </Td> </Tr> <Tr> <Th> March 3, 1845 </Th> <Td> Florida Territory was admitted as the twenty - seventh state, Florida . </Td> <Td> </Td> </Tr> <Table> <Tr> <Th> Date </Th> <Th> Event </Th> <Th> Change Map </Th> </Tr> <Tr> <Th> December 29, 1845 </Th> <Td> The Republic of Texas was annexed and admitted as the twenty - eighth state, Texas . Texas brought with it a substantial territorial dispute with Mexico . While many sources state that Mexico recognized the independence of the eastern portion of Texas, the treaties were rejected by the Mexican government . Texas formally handed over sovereignty to the United States in a ceremony on February 19, 1846 . The annexation led to the beginning of the Mexican--American War a few months later . </Td> <Td> Disputes: </Td> </Tr> <Tr> <Th> June 15, 1846 </Th> <Td> The Oregon Treaty established the 49th parallel north west of the Lake of the Woods as the continental border (so it did not include Vancouver Island) with land held by the United Kingdom . The sharing of Oregon Country ended, and the United States portion became unorganized territory . <P> The treaty was vague on which strait should be the border between Vancouver Island and the continent, thus causing a dispute over ownership of the San Juan Islands . It specified "through the middle of the said channel and of Fuca Straits, to the Pacific Ocean". </P> </Td> <Td> Northwestern North America: Disputes: </Td> </Tr> <Tr> <Th> September 22, 1846 </Th> <Td> Following the capture on August 18, 1846, of Santa Fe, the capital of the Mexican territory of Santa Fe de Nuevo México, a code of laws known as the Kearny Code was created for the area . The region overlapped with Texas' claim, though Texas had little to no control over the area outside of its eastern quarter . </Td> <Td> Unofficial change: </Td> </Tr> <Tr> <Th> December 28, 1846 </Th> <Td> The southern portion of Iowa Territory, south of parallel 43 ° 30 ′ north and east of the Big Sioux River, was admitted as the twenty - ninth state, Iowa . The remainder became unorganized territory . </Td> <Td> </Td> </Tr> <Tr> <Th> March 13, 1847 </Th> <Td> The District of Columbia retroceded Alexandria County back to Virginia . Congress passed the act on July 9, 1846, residents of Alexandria County were proclaimed by the president to have agreed to it on September 7, 1846, and Virginia took possession of the land on this date . </Td> <Td> </Td> </Tr> <Tr> <Th> May 29, 1848 </Th> <Td> The southern bulk of Wisconsin Territory, mainly east of the St. Croix River, was admitted as the thirtieth state, Wisconsin . The remainder became unorganized territory . However, the citizens of the remainder decided to continue on with a civil government, and even elected a delegate to the United States House of Representatives who would be seated on January 15, 1849, essentially making this region a de facto continuation of Wisconsin Territory . </Td> <Td> </Td> </Tr> <Tr> <Th> July 4, 1848 </Th> <Td> The Treaty of Guadalupe Hidalgo ended the Mexican--American War and ceded a large parcel of land from Mexico, consisting of its territories of Alta California and Santa Fe de Nuevo México, and its claim to Texas . Due to a disagreement over the southern border of Santa Fe de Nuevo México, a border dispute began . </Td> <Td> Disputes: </Td> </Tr> <Tr> <Th> August 14, 1848 </Th> <Td> Oregon Territory was organized from the unorganized territory that was formerly part of Oregon Country . </Td> <Td> </Td> </Tr> <Tr> <Th> February 13, 1849 </Th> <Td> The boundary dispute between Iowa and Missouri known as the Honey War was resolved by the Supreme Court of the United States . The resulting border was the Sullivan Line that existed before the dispute, roughly splitting the two claims . </Td> <Td> </Td> </Tr> <Tr> <Th> March 3, 1849 </Th> <Td> Minnesota Territory was organized from unorganized territory east of the Missouri River and the region that had been operating as de facto Wisconsin Territory . </Td> <Td> </Td> </Tr> <Tr> <Th> March 12, 1849 </Th> <Td> A local government formed the State of Deseret and claimed a vast portion of the southwest, including most of the Mexican Cession . Though it petitioned to be admitted to the United States, the proposal was rejected and, in 1850, Utah Territory was formed instead . The claimed area overlapped slightly with Texas' claimed area, as well as part of Oregon Territory . </Td> <Td> Unofficial change: </Td> </Tr> <Tr> <Th> September 9, 1850 </Th> <Td> The western portion of the Mexican Cession, west of the 120th meridian west, a diagonal line from where that intersects the 39th parallel north to where the Colorado River intersects the 35th parallel north, and the Colorado River, was admitted as the thirty - first state, California . The portion of the remainder north of the 37th parallel north and west of the summit of the Rocky Mountains was organized as Utah Territory . Part of Utah Territory overlapped with the portion of Texas that would be purchased on December 13, 1850, but the law authorizing the purchase was passed on this day, so the borders of Utah Territory assumed the purchase will go through . </Td> <Td> </Td> </Tr> <Tr> <Th> December 9, 1850 </Th> <Td> The United Kingdom ceded less than one acre of underwater rock known as Horseshoe Reef in Lake Erie near Buffalo, New York for a lighthouse . It was surrounded by British waters, thus creating a form of enclave . </Td> <Td> </Td> </Tr> <Tr> <Th> December 13, 1850 </Th> <Td> The federal government purchased the western claims of Texas . New Mexico Territory was organized from the part of this land east of the Rio Grande, along with the remaining unorganized territory from the Mexican Cession . New Mexico Territory included all of the area that had been governed under the Kearny Code . </Td> <Td> </Td> </Tr> <Tr> <Th> April 5, 1851 </Th> <Td> The State of Deseret dissolved itself, its functions and territory largely having been superseded by Utah Territory . </Td> <Td> Unofficial change: </Td> </Tr> <Tr> <Th> March 2, 1853 </Th> <Td> Washington Territory was organized from the half of Oregon Territory north of the 46th parallel north and the Columbia River . </Td> <Td> </Td> </Tr> <Tr> <Th> May 30, 1854 </Th> <Td> Kansas Territory was organized from unorganized territory north of the 37th parallel north, and Nebraska Territory was organized north of 40th parallel north . Much of the remaining unorganized territory, east of the 100th meridian west, became known as Indian Territory, designated as a place to resettle Indian tribes . <P> A small strip between the Texas Panhandle and Kansas Territory was unclaimed, due to falling south of Kansas Territory's border but north of the 36 ° 30 ′ latitude established in the Missouri Compromise as the northern limit of slavery, and thus Texas could not have it . This became known as the Public Land Strip, or sometimes "No Man's Land". </P> </Td> <Td> </Td> </Tr> <Tr> <Th> June 30, 1854 </Th> <Td> The United States purchased a large parcel from Mexico known as the Gadsden Purchase, as it offered a much better route for a southern transcontinental railroad . This resolved the border dispute, since the disputed land was included in the purchase . The purchase was defined as: starting from where the Rio Grande crosses parallel 31 ° 47' north; then west 100 miles; then south to parallel 31 ° 20' north; then west to the 111th meridian west; then a line from there to a point on the Colorado River 20 miles below the mouth of the Gila River; and the Colorado River . </Td> <Td> Disputes: </Td> </Tr> <Tr> <Th> August 4, 1854 </Th> <Td> The recently obtained Gadsden Purchase was assigned to New Mexico Territory . </Td> <Td> </Td> </Tr> <Tr> <Th> January 11, 1855 </Th> <Td> Due to its remote location, Boston Corner was transferred from Massachusetts to New York . </Td> <Td> </Td> </Tr> <Tr> <Th> March 6, 1855 </Th> <Td> The Supreme Court ruled in favor of Florida in a boundary dispute with Georgia, setting the state boundary line along McNeil's line . </Td> <Td> no change to map </Td> </Tr> <Tr> <Th> October 28, 1856 </Th> <Td> Baker Island and Jarvis Island were claimed under the Guano Islands Act . </Td> <Td> Pacific Ocean: </Td> </Tr> <Tr> <Th> May 11, 1858 </Th> <Td> The half of Minnesota Territory east of the Red River of the North, the Bois de Sioux River, and a line south from the southern tip of Big Stone Lake, was admitted as the thirty - second state, Minnesota . The remainder became unorganized territory . </Td> <Td> </Td> </Tr> <Tr> <Th> August 31, 1858 </Th> <Td> Navassa Island was claimed under the Guano Islands Act . </Td> <Td> Caribbean Sea: </Td> </Tr> <Tr> <Th> December 3, 1858 </Th> <Td> Howland Island was claimed under the Guano Islands Act . </Td> <Td> Pacific Ocean: </Td> </Tr> <Tr> <Th> February 14, 1859 </Th> <Td> The half of Oregon Territory west of the Snake River and a line south from the mouth of the Owyhee River was admitted as the thirty - third state, Oregon . The remainder was transferred to Washington Territory . </Td> <Td> </Td> </Tr> <Tr> <Th> July 6, 1859 </Th> <Td> A team of surveyors created the "Middleton Offset," a small notch in the border between Kentucky and Tennessee . It is unknown exactly why this was done . </Td> <Td> </Td> </Tr> <Tr> <Th> September 6, 1859 </Th> <Td> Johnston Atoll was claimed under the Guano Islands Act, though it had been claimed by Hawaii in 1858 . </Td> <Td> Pacific Ocean: </Td> </Tr> <Tr> <Th> November 7, 1859 </Th> <Td> A local government was set up encompassing parts of the territories of Kansas, Nebraska, New Mexico, Utah, and Washington, with the name of Jefferson Territory, bounded by the 37th and 43rd parallels north, and 102nd and 110th meridians west . While never recognized by the federal government, it generally held control over the area until Colorado Territory was established, which adopted most of its laws . </Td> <Td> Unofficial change: </Td> </Tr> <Tr> <Th> December 27, 1859 </Th> <Td> Enderbury Island, McKean Island, Phoenix Island, and Starbuck Island were claimed under the Guano Islands Act . </Td> <Td> Pacific Ocean: </Td> </Tr> <Tr> <Th> December 29, 1859 </Th> <Td> Christmas Island and Malden Island were claimed under the Guano Islands Act . </Td> <Td> Pacific Ocean: </Td> </Tr> <Tr> <Th> February 8, 1860 </Th> <Td> Texas created Greer County, claiming part of Indian Territory based on a different understanding from the federal government of which river was the border between the two . <P> Atafu, Birnie Island, Butaritari, Caroline Island, Fanning Island, Flint Island, Gardner Island, Canton Island, Kingman Reef, Manihiki, Marakei, Nukunono, Palmyra Atoll, Penrhyn, Pukapuka, Rakahanga, Swains Island, Sydney Island, Vostok Island, and Washington Island were all claimed under the Guano Islands Act . Many additional islands were listed as bonded on this date, but based on the coordinates they were either phantoms or duplicates . In addition, Sarah Ann Island was claimed, which may have existed and would be sighted as late as 1917, but has since disappeared . </P> </Td> <Td> Pacific Ocean: </Td> </Tr> </Table> <Tr> <Th> Date </Th> <Th> Event </Th> <Th> Change Map </Th> </Tr>

What gave the us the last land needed to expand to the pacific ocean