July 1866

Tuesday 03:

Austro-Prussian War decided at Battle of Königgratz, resulting in Prussia taking over as the prominent German nation from Austria.

Friday 20:

The Austrian navy, led by Admiral Wilhelm von Tegetthoff, defeats the Italian navy near the island of Vis.

Tuesday 24:

Reconstruction: Tennessee becomes the first U.S. state to be readmitted to the Union following the American Civil War.

Wednesday 25:

The U.S. Congress passes legislation authorizing the rank of General of the Army (now called "5-star general") Lieutenant General Ulysses S. Grant becomes the first to have this rank.

Friday 27:

The Atlantic Cable is successfully completed, allowing transatlantic telegraph communication for the first time.

Saturday 28:

The Metric Act of 1866 becomes law and legalizes the standardization of weights and measures in the United States.