Here are some notable events that occurred worldwide on April 12th before the year 2020:

1861: The American Civil War began when Confederate forces fired on Fort Sumter in South Carolina, marking the start of hostilities between the North and South.

1934: The strongest surface wind speed ever recorded on Earth was measured at 231 miles per hour (372 km/h) on Mount Washington, New Hampshire, USA.

1945: President Franklin D. Roosevelt, who led the United States through most of World War II, passed away in Warm Springs, Georgia, USA.
1955: The Salk polio vaccine, developed by Dr. Jonas Salk, was declared safe and effective, leading to widespread vaccination efforts against polio.
1961: Soviet cosmonaut Yuri Gagarin became the first human to travel into space aboard the Vostok 1 spacecraft, orbiting the Earth once before safely returning.
1963: Civil rights leader Martin Luther King Jr. was arrested during a demonstration in Birmingham, Alabama, where he wrote his famous "Letter from Birmingham Jail."
1966: The Soviet Luna 10 spacecraft entered orbit around the Moon, becoming the first spacecraft to orbit the Moon and transmit data back to Earth.
1980: The United States severed diplomatic relations with Iran and imposed economic sanctions after the U.S. Embassy in Tehran was seized by Iranian militants in November 1979.
1981: The first space shuttle mission, STS-1 (Columbia), was launched by NASA. Astronauts John W. Young and Robert L. Crippen piloted the spacecraft.
1981: The maiden flight of the Space Shuttle Columbia (STS-1) took place, marking the beginning of NASA's Space Shuttle program.
1990: Jim Gary, an American sculptor known for creating large dinosaur sculptures from discarded automobile parts, passed away at the age of 56.
2009: The International Criminal Court (ICC) issued an arrest warrant for Sudanese President Omar al-Bashir on charges of war crimes and crimes against humanity in Darfur.
These are just a few examples of significant events that happened on April 12th in history. Each year and era brings its own unique events and developments.