- Bloodiest single-day battle in American history: ~23,000 casualties
- Union victory - stopped 1st Confederate invasion of the North and boosted Northern morale
- Emancipation Proclamation: issued by Lincoln shortly after Antietam
- Marked turning point in Civil War- the South would never again invade the North with a major campaign
- Strengthened Lincoln's hand when dealing with foreign nations as his political prestige improved
- Indirectly led to Gettysburg Address the following July - helped change Union war aims from preservation of the Union to include ending slavery