April 9

French explorer René-Robert Cavelier, Sieur de La Salle, reaches the mouth of the Mississippi River and claims the region for France, naming it Louisiana.

French explorer René-Robert Cavelier, Sieur de La Salle, traveled down the Mississippi River to its mouth at the Gulf of Mexico and formally claimed the entire river basin for France, naming the vast territory Louisiana in honor of King Louis XIV. The claim, covering land that would later become parts of more than a dozen U.S. states, shaped French colonial ambitions in North America for the following century.

King George III ratifies the Treaty of Paris, formally ending the American Revolutionary War.

King George III ratified the Treaty of Paris, the formal peace agreement ending the American Revolutionary War and recognizing the independence of the thirteen former colonies as the United States of America. The treaty also established generous boundaries for the new nation, stretching to the Mississippi River, and addressed issues including fishing rights, debts, and the treatment of Loyalists.

Confederate General Robert E. Lee surrenders the Army of Northern Virginia to Union General Ulysses S. Grant at Appomattox Court House, effectively ending the Civil War.

After a grueling four-year war, Confederate General Robert E. Lee surrendered the remnants of his once-formidable Army of Northern Virginia to Union General Ulysses S. Grant at Appomattox Court House, effectively ending the American Civil War. Grant's generous surrender terms, allowing Confederate soldiers to return home without punishment, helped set a tone for reconciliation, even as the deeper work of Reconstruction remained far from resolved.

The Battle of Arras begins on the Western Front, including the Canadian Corps' assault on Vimy Ridge.

British and Canadian forces launched the Battle of Arras on the Western Front, including a highly successful assault by the Canadian Corps to capture the heavily fortified German position at Vimy Ridge. The victory, achieved through careful planning and coordinated artillery tactics, came at a heavy cost but is remembered as a defining moment in the development of a distinct Canadian national identity.

Singer Marian Anderson performs an open-air concert at the Lincoln Memorial after being denied use of Constitution Hall because she was Black.

After the Daughters of the American Revolution refused to let contralto Marian Anderson perform at Constitution Hall because she was Black, First Lady Eleanor Roosevelt helped arrange an alternative open-air concert at the Lincoln Memorial. Anderson performed before a crowd of 75,000 people and a radio audience of millions, in a moment widely remembered as an early landmark of the civil rights movement.

Nazi Germany invades Denmark and Norway in Operation Weserübung.

Nazi Germany launched simultaneous invasions of Denmark and Norway under the codename Operation Weserübung, aiming to secure iron ore shipping routes and strategic naval bases in the North Atlantic. Denmark surrendered within hours, while Norway mounted stronger resistance with British and French support before ultimately falling to German occupation after a two-month campaign.

Lutheran pastor and anti-Nazi dissident Dietrich Bonhoeffer is executed by the Nazis just weeks before Germany's surrender.

Lutheran pastor and theologian Dietrich Bonhoeffer, who had joined a conspiracy to assassinate Adolf Hitler and was imprisoned for his role, was executed by hanging at the Flossenbürg concentration camp just weeks before the camp's liberation by Allied forces. Bonhoeffer's writings on faith and resistance to tyranny have made him one of the most influential Christian theologians of the 20th century.

NASA introduces the "Mercury Seven," the first group of American astronauts selected for spaceflight.

NASA publicly introduced the "Mercury Seven," the first group of American astronauts selected for the country's fledgling human spaceflight program, at a press conference that made instant national celebrities of the seven military test pilots. Their subsequent missions during Project Mercury, including Alan Shepard's and John Glenn's historic flights, captured the public imagination during the early Space Race with the Soviet Union.

Soviet troops violently disperse a pro-independence demonstration in Tbilisi, Georgia, killing at least 20 people.

Soviet troops violently dispersed a peaceful pro-independence demonstration in Tbilisi, the capital of Soviet Georgia, using sharpened shovels and toxic gas against unarmed protesters, killing at least 20 people, most of them young women. The massacre outraged Georgians and became a significant catalyst for the republic's independence movement as the Soviet Union began to unravel over the following two years.

American forces capture Baghdad during the Iraq War, symbolized by the toppling of a large statue of Saddam Hussein.

American forces advanced into central Baghdad, and jubilant crowds, assisted by U.S. Marines, toppled a large statue of Saddam Hussein in Firdos Square, an image broadcast worldwide as a symbol of the collapse of his government during the initial invasion phase of the Iraq War. The moment, however, obscured the far longer and more difficult occupation and insurgency period that followed.