<a href="https://en.wikipedia.org/wiki/American_Civil_War" id="mwjA" rel="mw:WikiLink" title="American Civil War">American Civil War</a>: <a href="https://en.wikipedia.org/wiki/George_B._McClellan" id="mwjQ" rel="mw:WikiLink" title="George B. McClellan">George B. McClellan</a>'s <a href="https://en.wikipedia.org/wiki/Army_of_the_Potomac" id="mwjg" rel="mw:WikiLink" title="Army of the Potomac">Army of the Potomac</a> halts the first <a href="https://en.wikipedia.org/wiki/Maryland_campaign" id="mwjw" rel="mw:WikiLink" title="Maryland campaign">invasion</a> of the <a href="https://en.wikipedia.org/wiki/Northern_United_States#American_Civil_War" id="mwkA" rel="mw:WikiLink" title="Northern United States">North</a> by <a href="https://en.wikipedia.org/wiki/Robert_E._Lee" id="mwkQ" rel="mw:WikiLink" title="Robert E. Lee">Robert E. Lee</a> and his <a href="https://en.wikipedia.org/wiki/Army_of_Northern_Virginia" id="mwkg" rel="mw:WikiLink" title="Army of Northern Virginia">Army of Northern Virginia</a> in the single-day <a href="https://en.wikipedia.org/wiki/Battle_of_Antietam" id="mwkw" rel="mw:WikiLink" title="Battle of Antietam">Battle of Antietam</a>, the bloodiest day in American military history.<sup about="#mwt54" class="mw-ref reference" data-mw='{"name":"ref","attrs":{},"body":{"id":"mw-reference-text-cite_note-9"}}' id="cite_ref-9" rel="dc:references" typeof="mw:Extension/ref"><a href="./September_17#cite_note-9" id="mwlA" style="counter-reset: mw-Ref 9;"><span class="mw-reflink-text" id="mwlQ">[9]</span></a></sup>
<span class="mw-reference-text" id="mw-reference-text-cite_note-9"><cite about="#mwt51" class="citation web cs1" id="mwCG8"><a class="external text" href="http://npshistory.com/brochures/anti/battle-history.pdf" id="mwCHA" rel="mw:ExtLink nofollow">"The Battle of Antietam"</a> <span class="cs1-format" id="mwCHE">(PDF)</span>. <i id="mwCHI">NPSHistory.com</i>. National Park Service<span class="reference-accessdate" id="mwCHM">. Retrieved <span class="nowrap" id="mwCHQ">June 3,</span> 2024</span>.</cite><span about="#mwt51" class="Z3988" id="mwCHU" title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&amp;rft.genre=unknown&amp;rft.jtitle=NPSHistory.com&amp;rft.atitle=The+Battle+of+Antietam&amp;rft_id=http%3A%2F%2Fnpshistory.com%2Fbrochures%2Fanti%2Fbattle-history.pdf&amp;rfr_id=info%3Asid%2Fen.wikipedia.org%3ASeptember+17"></span></span>