The Jews who were dying in the desert for forty years stopped dying on this day.
The prohibition to give wives to the Binyamin tribe - which resulted from the incident at Givah - was annulled on that day, and Jews were reunited.
The prohibition to go to Jerusalem, established by Yaravam ben Nevat, was removed.
The slain people of Bethar, who were killed on Tisha B'Av, were allowed to be buried. This happened on Tu B'Av, three years later. The other miracle was that the bodies did not decompose.
Art: A Jewish Wedding by Joseph Israƫls