Final answer:
Lincoln delayed the Emancipation Proclamation for strategic reasons, awaiting a Union victory and deeming emancipation a military necessity and diplomatic tool. Despite opposition, he issued it following the Battle of Antietam to strengthen its impact and shift the war's purpose.
Step-by-step explanation:
President Abraham Lincoln delayed the issuance of the Emancipation Proclamation due to several strategic considerations. A pivotal factor was timing; Lincoln waited for a significant Union victory, which came with the Battle of Antietam, to strengthen the proclamation's impact. This victory provided the momentum needed to issue the preliminary proclamation on September 22, 1862. For Lincoln, emancipation was also a military necessity, weakening the Confederacy by depriving it of slave labor. Another reason was diplomatic; he knew that making the eradication of slavery a goal of the Union's war efforts would make British support for the Confederacy more difficult due to Britain's anti-slavery stance. Despite political opposition and the divisive nature of slavery, Lincoln moved ahead with the proclamation, which he saw as crucial to preserve the Union and ultimately, reshaped the purpose of the Civil War.