American Civil War ndash Andrew's Raid - Union volunteers steal a Confederate locomotive, setting off The Great Locomotive Chase, famously involving the use of "The General" steam locomotive, which still exists in the 21st century.
Friday, April 12, 1861
The American Civil War begins with the bombardment of Fort Sumter, South Carolina.
Margaret Porteous is the first person recorded to die in the Great Plague of London. This last major outbreak of Bubonic plague in the British Isles was possibly introduced by Dutch prisoners of war. Two-thirds of Londoners leave the city, but over 68,000 die. Plague spreads to Derby.
Sunday, April 12, 1654
Oliver Cromwell creates a union between England and Scotland, with Scottish representation in the Parliament of England.ref name=Cassell's Chronology/
Karl Sverkersson is murdered by Knut Eriksson (son of Eric Jedvardsson), who proclaims himself king of Sweden. However, Karl's half brothers Kol and Boleslaw proclaim themselves kings of Östergötland, in opposition to Knut, which leads to fights for the power in Sweden until 1173.
Emperor Leo I has his general Anthemius elected emperor of the Western Roman Empire. He allies himself with Ricimer, "de facto" ruler of Rome, and marries his daughter Alypia to him. This to strengthen the relationship and end the hostilities between the Eastern and Western Empire.