Today marks the 145th anniversary of the Fall of Vicksburg (Mississippi), a critical victory for U.S. Grant and the Union Army. After a siege which had begun in May, the final surrender of the city to Grant marked the fall of the last major Confederate stronghold on the Mississippi River. With the Union victory, the Confederacy was essentially divided into two and the major transportation route for the rebels fell into the North's hands.
The days of July 1-4, 1863 marked the major turning point of the war for the Union. Only July 1-3, the Union won a critical victory in Gettysburg, Pennsylvania and then the jubliant news came a day later from Vicksburg when that city finally surrendered.
Abraham Lincoln is famous for his brilliant speeches at Gettysburg, and his two inaugural addresses. But his single sentence statement after the hard-fought seige of Vicksburg is perhaps the most stunning line he ever wrote: "The Father Of Waters again goes unvexed to the sea."
To learn more about the Siege and Fall of Vicksburg, here is a great link. Another article from the National Park Service provides further background.