Peter Joseph Osterhaus was a German-American Union Army general in the American Civil War and later served as a diplomat.

The Battle of Big Black River Bridge was fought on May 17, 1863, as part of the Vicksburg Campaign of the American Civil War. During the war, the city of Vicksburg, Mississippi, was a key point on the Mississippi River. On April 30, 1863, a Union army commanded by Major General Ulysses S. Grant began crossing onto the east side of the Mississippi River as part of a campaign against Vicksburg. After engaging and defeating Confederate forces in several intermediate battles, Grant's army defeated Lieutenant General John C. Pemberton's Confederates at the decisive Battle of Champion Hill on May 16. During the retreat from Champion Hill, one division of Pemberton's army, commanded by Major General William W. Loring, was cut off from Pemberton's main body. Pemberton did not know the location of Loring's division, and he held a bridgehead on the east side of the Big Black River to cover Loring's anticipated withdrawal across the river on the morning of May 17.