United States

=== Civil War ===
{{Main|History of the United States (1849–1865)|American Civil War}}
[[File:US map 1864 Civil War divisions.svg|thumb|Division of the states during the [[American Civil War]]:
{{legend|#204A87|[[Union (American Civil War)|Union states]]}}
{{legend|#729FCF|[[Border states (American Civil War)|Border states]]}}
{{legend|#A40000|[[Confederate States of America|Confederate states]]}}
{{legend|#D3D7CF|[[Territories of the United States|Territories]]}}]]

During the colonial period, [[Slavery in the colonial history of the United States|slavery was legal in the American colonies]], though the practice began to be significantly questioned during the American Revolution.{{sfnm|1a1=Walker Howe|1y=2007|1p=52–54|2a1=Wright|2y=2022}} States in [[Northern United States|The North]] enacted [[Abolitionism in the United States|abolition laws]],{{sfnm|1a1=Walker Howe|1y=2007|1p=52–54|2a1=Rodriguez|2y=2015|2p=XXXIV|3a1=Wright|3y=2022}} though support for slavery strengthened in [[Southern United States|Southern states]], as inventions such as the [[cotton gin]] made the institution increasingly profitable for [[Planter class|Southern elites]].<ref>[[United States#Walton|Walton, 2009]], p. 43</ref><ref>[[United States#Gordon|Gordon, 2004]], pp. 27,29</ref>{{sfn|Walker Howe|2007|p=478, 481–482, 587–588}} This [[Slave states and free states|sectional conflict]] regarding slavery [[Origins of the American Civil War|culminated]] in the [[American Civil War]] (1861–1865).<ref>{{cite book |last=Murray |first=Stuart |url=https://books.google.com/books?id=bJ_sy7mmmxQC&pg=PA76 |title=Atlas of American Military History |publisher=Infobase Publishing |year=2004 |isbn=978-1-4381-3025-5 |page=76 |access-date=October 25, 2015}} {{cite book |last=Lewis |first=Harold T. |url=https://books.google.com/books?id=kr-xNru5vZkC&pg=PA53 |title=Christian Social Witness |publisher=Rowman & Littlefield |year=2001 |isbn=978-1-56101-188-9 |page=53}}</ref><ref name="Woods 2012 pp. 415–4392">{{cite journal |last=Woods |first=Michael E. |year=2012 |title=What Twenty-First-Century Historians Have Said about the Causes of Disunion: A Civil War Sesquicentennial Review of the Recent Literature |url=http://www.jstor.org/stable/44306803 |journal=The Journal of American History |publisher=[Oxford University Press, Organization of American Historians] |volume=99 |issue=2 |pages=415–439 |doi=10.1093/jahist/jas272 |issn=0021-8723 |jstor=44306803 |access-date=April 29, 2023}}</ref>

Eleven slave states [[seceded]] and formed the [[Confederate States of America]], while the other states remained in [[Union (American Civil War)|the Union]].<ref name="Silkenat 2019 p. 252">{{cite book |last=Silkenat |first=D. |url=https://books.google.com/books?id=nHWKDwAAQBAJ&pg=PA25 |title=Raising the White Flag: How Surrender Defined the American Civil War |publisher=University of North Carolina Press |year=2019 |isbn=978-1-4696-4973-3 |series=Civil War America |page=25 |access-date=April 29, 2023}}</ref> War broke out in April 1861 after the Confederacy [[Battle of Fort Sumter|bombarded Fort Sumter]].<ref>{{cite book |last=Vinovskis |first=Maris |title=Toward A Social History of the American Civil War: Exploratory Essays |date=1990 |publisher=Cambridge University Press |isbn=978-0-521-39559-5 |location=Cambridge; New York |page=4}}</ref> After the January 1863 [[Emancipation Proclamation]], many freed slaves joined the Union Army.<ref>{{cite web|url=https://www.archives.gov/education/lessons/blacks-civil-war/ |title=The Fight for Equal Rights: Black Soldiers in the Civil War|work=[[National Archives and Records Administration|U.S. National Archives and Records Administration]]|date=August 15, 2016|quote=By the end of the Civil War, roughly 179,000 black men (10% of the Union Army) served as soldiers in the U.S. Army and another 19,000 served in the Navy.}}</ref> The war [[Turning point of the American Civil War|began to turn in the Union's favor]] following the 1863 [[Siege of Vicksburg]] and [[Battle of Gettysburg]], and the Confederacy surrendered in 1865 after the Union's victory in the [[Battle of Appomattox Court House]].<ref>Davis, Jefferson. [https://archive.org/stream/ashorthistoryco00davigoog#page/n544/mode/2up/search/surrender+at+Appomattox ''A Short History of the Confederate States of America''], 1890, 2010. {{ISBN|978-1-175-82358-8}}. Available free online as an ebook. Chapter LXXXVIII, "Re-establishment of the Union by force", p. 503. Retrieved March 14, 2012.</ref>

The [[Reconstruction era]] followed the war. After [[Assassination of Abraham Lincoln|the assassination]] of President [[Abraham Lincoln]], [[Reconstruction Amendments]] were passed to [[Civil rights movement (1865–1896)|protect the rights of African Americans]]. National infrastructure, including [[First transcontinental telegraph|transcontinental telegraph]] and [[First transcontinental railroad|railroads]], spurred growth in the [[American frontier]].<ref name="Black2011kj2">{{cite book |last=Black |first=Jeremy |url=https://books.google.com/books?id=EIst_CSWOqIC&pg=PA275 |title=Fighting for America: The Struggle for Mastery in North America, 1519–1871 |publisher=Indiana University Press |year=2011 |isbn=978-0-253-35660-4 |page=275 |author-link=Jeremy Black (historian)}}</ref>