April 1 ( ):
- 1969 – The Libertarian Forum, with Murray N. Rothbard as a founding editor, published its first full issue.
April 2 ():
- 1792 - The Coinage Act of 1792 was passed into law in the United States, which declared the silver dollar as the country's unit of currency, and established the US Mint.
April 3 ():
- 1449 – A maker of stained glass, John of Utynam, received the first known English patent, granting him a 20-year monopoly.
April 4 ():
- 1917 – With encouragement from President Woodrow Wilson, the US Congress declared war on Germany, leading the country into World War I.
- 1949 – The North Atlantic Treaty Organization ("NATO") was founded, with the intent to "to keep the Russians out, the Americans in, and the Germans down."
April 5 ():
- 1933 – President Franklin D. Roosevelt issued an executive order prohibiting the private ownership of gold.
April 6 ():
- 1917 – The United States entered World War I after President Woodrow Wilson successfully urged congress to declare war on Germany.
April 7 ():
- 1994 – The Rwandan Genocide began near Kigali, Rwanda, ultimately resulting in the deaths of as many as a million people.
April 8 ():
- 1895 – The US Supreme Court ruled that unapportioned income taxes were unconstitutional.
- 1943 – US President Franklin D. Roosevelt issued a "hold-the-line" executive order, establishing price controls, wage limits, and restrictions on labor mobility.
April 9 ():
- 1865 – Robert E. Lee surrendered the Army of Northern Virginia to Ulysses S. Grant, opting not to encourage guerrilla warfare.
April 10 ():
- 1710 – The first copyright law, the Statute of Anne, went into effect, restricting the reproduction of books.
- 1947 – The Mount Pelerin Society was founded, with members including Friedrich Hayek, Ludwig von Mises, George Stigler and Milton Friedman.
April 11 ():
- 1979 – Ugandan dictator Idi Amin was deposed and exiled in the face of domestic and regional military opposition.
April 12 ():
- 1861 – Confederate soldiers fired on South Carolina's Fort Sumter after U. S. Army troops refused to abandon the fort and the state, thereby starting the War Between the States.
- 2009 – After several years of severe hyperinflation, the Zimbabwean dollar was officially abandoned.
- 2010 – The Mises Academy offers its first course, taught by Robert Murphy and entitled "Understanding the Business Cycle."
April 13 ():
April 14 ():
- 2002 – Hugo Chavez regained power in Venezuela after being ousted by the country's military two days earlier.
April 15 ():
- 1989 – Chinese students began going to Tiananmen Square to mourn the death of Hu Yaobang, a party official tolerant of dissent, setting the stage for the Tiananmen Square massacre.
April 16 ():
- 2003 – The Treaty of Accession was signed, adding ten new countries to the European Union, including the Czech Republic, Cyprus, Hungary, and Poland.
April 17 ():
- 1854 – Individualist Anarchist Benjamin Tucker was born.
- 1961 – Cuban exiles, with US backing, invaded Cuba at the Bay of Pigs in a failed attempt to overthrow Fidel Castro.
April 18 ():
April 19 ():
- 1772 – David Ricardo, British Economist, was born.
- 1775 – British soldiers attempting to confiscate arms in Concord, Massachusetts were defeated by militia.
- 1861 – In the first bloodshed of the American Civil War, a brawl broke out between militia from Massachusetts and Confederate sympathizers in Baltimore.
- 1943 – German troops invaded the Warsaw Ghetto, but Jewish insurgents held them off for nearly a month.
April 20 ():
April 21 ():
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April 23 ():
- 1898 – Spain declared war on the United States in response to US demands that Spain abandon its colony, Cuba.
April 24 ():
April 25 ():
- 1898 – The United States declared war on Spain after the Spanish refused to abandon Cuba, one of their colonies.
April 26 ():
- 1979 – The United States Treasury failed to make payments on maturing Treasury bills, marking the first US default since 1933.
April 27 ():
- 1861 – President Abraham Lincoln suspended the writ of habeas corpus in Maryland and elsewhere, in order to quell riots and prevent Maryland from seceding.
April 28 ():
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April 30 ():
- 1803 – The United States purchased a vast wilderness west of the Mississippi River, raising constitutional questions.
- 1975 – US military and civilian personnel evacuated as Saigon was captured by North Vietnamese forces, ending the Vietnam War.