4月 was a month.
By year
19th century
In 1861 South Carolina passed a kind of "Declaration of Independence" from the United States, in many ways beginning the American Civil War. The war also ended in 4月 1865, with Abraham Lincoln giving a victorious speech at Richmond, Virginia in the early part of the month. Despite the Fifth Doctor saving him from assassination there, Lincoln would be killed by John Wilkes Booth that 4月14日. Many ordinary citizens wrote letters throughout the month about Lincoln's fate, and about the future of the United States and the former Confederacy. Many letters, newspaper articles and diary entries were written by ordinary Americans — such as Will Johnson, Claire Bartlett, Hilary Makepeace and Kenneth Smith — during both of these fateful 4月s. Additionally, Paul LeVal was pressed into service in the Confederate Army, as were many southerners, during 4月 1861. (PROSE: Blood and Hope)
20th century
In 1941, Nazi Germany invaded Greece during World War II and clashed with the British. The latter was outflanked on the Pindus Mountains on 4月19日 and was forced to withdraw from Greece on 4月23日. (PROSE: Just War)
In 1945, the Soviet Union pushed towards Berlin for a final assault on the heart of the Third Reich. More leading Nazis retreated to the Führerbunker. Shortly after Hitler's 56th birthday on 4月20日, the Red Army reached the outskirts of Berlin and clawed their way to the Zitadelle. More and more Nazis began to abandon Hitler, who eventually committed suicide on 4月30日. His wife, Eva Braun, secretly made her escape with their unborn child, leaving Germany before the British Army took Hamburg. (PROSE: The Shadow in the Glass)
In 1948, the Fourth Doctor returned numerous lost paintings and treasures to Father Antonio in Borosini, Italy. He had previously taken these valuables away in the TARDIS in the summer of 1944 to prevent them from falling into German hands. (COMIC: Treasure Trail)
In 1963, The Cold extended an unnatural winter into 4月, leading to riots, communications disruptions and deaths throughout London. It was lifted on 4月4日 once the First Doctor intervened. (PROSE: Time and Relative)