| 38521 | April 4 | Event | 1812 – United States President James Madison enacts a ninety-day embargo on trade with the United Kingdom. |
| 38522 | April 4 | Event | 1814 – Napoleon abdicates for the first time and names his son Napoleon II as Emperor of the French. |
| 38523 | April 4 | Event | 1818 – The United States Congress adopts the flag of the United States with 13 red and white stripes and one star for each state (then 20). |
| 38524 | April 4 | Event | 1841 – William Henry Harrison dies of pneumonia becoming the first President of the United States to die in office and with the shortest term served. Vice President John Tyler, becomes President upon Harrison's death. |
| 38525 | April 4 | Event | 1850 – The Great Fire of Cottenham: A large part of the Cambridgeshire village (England) is burnt to the ground in suspicious circumstances. |
| 38526 | April 4 | Event | 1850 – Los Angeles is incorporated as a city. |
| 38527 | April 4 | Event | 1859 – Bryant's Minstrels debut "Dixie" in New York City in the finale of a blackface minstrel show. |
| 38528 | April 4 | Event | 1865 – American Civil War: A day after Union forces capture Richmond, Virginia, U.S. President Abraham Lincoln visits the Confederate capital. |
| 38529 | April 4 | Event | 1866 – Alexander II of Russia narrowly escapes an assassination attempt by Dmitry Karakozov in the city of Saint Petersburg. |
| 38530 | April 4 | Event | 1873 – The Kennel Club is founded, the oldest and first official registry of purebred dogs in the world. |
| 38531 | April 4 | Event | 1887 – Argonia, Kansas elects Susanna M. Salter as the first female mayor in the United States. |
| 38532 | April 4 | Event | 1905 – In India, an earthquake hits the Kangra Valley, killing 20,000, and destroying most buildings in Kangra, McLeod Ganj and Dharamsala. |
| 38533 | April 4 | Event | 1913 – First Balkan War: Greek aviator Emmanouil Argyropoulos becomes the first pilot to die in the Hellenic Air Force when his plane crashes. |
| 38534 | April 4 | Event | 1925 – The Schutzstaffel (SS) is founded in Germany. |
| 38535 | April 4 | Event | 1930 – The Communist Party of Panama is founded. |
| 38536 | April 4 | Event | 1933 – U.S. Navy airship, USS Akron, is wrecked off the New Jersey coast due to severe weather. |
| 38537 | April 4 | Event | 1939 – Faisal II becomes King of Iraq. |
| 38538 | April 4 | Event | 1944 – World War II: First bombardment of oil refineries in Bucharest by Anglo-American forces kills 3000 civilians. |
| 38539 | April 4 | Event | 1945 – World War II: American troops liberate Ohrdruf forced labor camp in Germany. |
| 38540 | April 4 | Event | 1945 – World War II: American troops capture Kassel. |
| 38541 | April 4 | Event | 1945 – World War II: Soviet troops liberate Hungary from German occupation and occupy the country itself. |
| 38542 | April 4 | Event | 1949 – Twelve nations sign the North Atlantic Treaty creating the North Atlantic Treaty Organization. |
| 38543 | April 4 | Event | 1958 – The CND peace symbol is displayed in public for the first time in London. |
| 38544 | April 4 | Event | 1960 – France agrees to grant independence to the Mali Federation, a union of Senegal and French Sudan. |
| 38545 | April 4 | Event | 1964 – The Beatles occupy the top five positions on the Billboard Hot 100 pop chart. |
| 38546 | April 4 | Event | 1965 – The first model of the new Saab Viggen fighter aircraft is unveiled. |
| 38547 | April 4 | Event | 1967 – Martin Luther King Jr. delivers his "Beyond Vietnam: A Time to Break Silence" speech in New York City's Riverside Church. |
| 38548 | April 4 | Event | 1968 – Martin Luther King Jr. is assassinated by James Earl Ray at a motel in Memphis, Tennessee. |
| 38549 | April 4 | Event | 1968 – Apollo program: NASA launches Apollo 6. |
| 38550 | April 4 | Event | 1968 – A.E.K. Athens B.C. becomes the first Greek team to win the European Basketball Cup. |