May 31 - In the Fenian Invasion of Canada, John O'Neill leads 850 Fenian raiders across the Niagara River at Buffalo, New York/Fort Erie, Ontario, as part of an effort to free Ireland from the English. Canadian militia and British regulars repulse the invaders in over the next three days, at a cost of 9 dead and 38 wounded to the Fenian's 19 dead and about 17 wounded.
June 3 - Fenians are driven out of Fort Erie, Ontario, into the United States.
June 7 - 1,800 Fenian raiders are repelled back to the United States after they loot and plunder around Saint-Armand and Frelighsburg, Quebec.
June 11 - The Allahabad High Court (then Agra High Court) is established in India.
June 22 - Battle of Custoza: an Austrian army defeats the Italian army during the Austro-Prussian War.
July 3 - Austro-Prussian War is decided at the Battle of Königgratz, resulting in Prussia taking over as the prominent German nation from Austria.
July 24 - Reconstruction: Tennessee becomes the first U.S. State to be readmitted to the Union following the American Civil War.
July 25 - The U.S. Congress passes legislation authorizing the rank of General of the Army (commonly called "5-star general"). Lieutenant General Ulysses S. Grant becomes the first to be promoted to this rank.
July 27 - The Atlantic Cable is successfully completed, allowing transatlantic telegraph communication for the first time.
July 30 - New Orleans's Democratic government orders police to raid an integrated Republican Party meeting, killing 40 people and injuring 150.
August 20 - President Andrew Johnson formally declares the American Civil War over.
August 23 - Austro-Prussian War ends with the Treaty of Prague.
September 22 - Battle of Curupaity in the War of the Triple Alliance.