306 Constantine the Great, aka Constantine I is proclaimed Roman emperor by his troops, and is the first Christian Roman emperor, later becoming St. Constantine in the Eastern Orthodox church. He initiated a policy of religious tolerance, and ended Christian persecution. He also shifted the Roman capital from Rome to Constantinople,which remained the capital of the eastern Roman empire for a millenium.
1755 British governor Charles Lawrence and the Nova Scotia Council order the deportation of the Acadians. Thousands of Acadians are sent to the British Colonies in America, France and England. Some later move to Louisiana, while others resettle in New Brunswick. Those in Louisiana become known as 'Cajuns, short for Acadians. It was an attempt to remove the French settlers, a kind of ethnic cleansing. Approximately a third died. Acadia was renamed Nova Scotia or 'New Scotland' by the British.
1758 As part of the Seven Years' War: the island battery at Fortress Louisbourg in Nova Scotia is silenced and all French warships are destroyed or taken, as the English tried to drive the French out of the territory which became Canada.
1799 At Aboukir in Egypt, Napoleon I of France defeats 10,000 Ottomans under Mustafa Pasha, and was in turn defeated by the British under Admiral Horatio Nelson.
1837 – The first commercial use of an electric telegraph is successfully demonstrated by William Cooke and Charles Wheatstone on 25 July 1837 between Euston and Camden Town in London.
1898 – The United States invasion of Puerto Rico begins with U.S. troops led by General Nelson Miles landing at harbor of Guánica, Puerto Rico (The land invasion, proper, began that day: Sea-based bombardment and shelling of the capital city of San Juan had been occurring since May 1898).
1907 – Korea becomes a protectorate of Japan.
1909 – Louis Blériot makes the first flight across the English Channel in a heavier-than-air machine from (Calais to Dover) in 37 minutes.
1917 – Sir Thomas Whyte introduces the first income tax in Canada as a "temporary" measure (lowest bracket is 4% and highest is 25%).
1920 – The first transatlantic two-way radio broadcast takes place.
1934 – The Nazis assassinate Austrian Chancellor Engelbert Dollfuss in a failed coup attempt.
1973 – Soviet Mars 5 space probe launched.
1978 – Louise Brown, the world's first "test tube baby", conceived through in vitro fertilization, is born.
1979 – Another section of the Sinai peacefully returned by Israel to Egypt.
1993 – Israel launches a massive attack against terrorist forces in Lebanon in what the Israelis call Operation Accountability, and the Lebanese call Seven-Day War.
1994 – Israel and Jordan sign the Washington Declaration, which formally ends the state of war that had existed between the nations since 1948.
1995 A U.N. war crimes tribunal indicted Bosnian Serb leader Radovan Karadzic, army commander Gen. Ratko Mladic, and 22 other Serbs for war crimes.