- Apr 4 Congress decides on the US flag: 13 red & white stripes & 20 stars
Battle of Maipú
Apr 5 Battle of Maipú: Chile's independence movement led by Bernardo O'Higgins and José de San Martín win a decisive victory over Spain, leaving 2,000 Spaniards and 1,000 Chilean patriots dead
First Seminole War
Apr 7 General Andrew Jackson conquers Spanish Fort San Marcos (St Marks), in Spanish Florida during his pursuit of the Native American Seminole Tribe, in what would become known as the First Seminole War
- Apr 21 Franz Grillparzer's "Sappho" premieres in Vienna
US-Canada Border Treaty
Apr 28 Rush-Bagot treaty signed between US President James Monroe and Great Britain, demilitarizing the US-Canada border [1]