What was the significance of the battle at Fort Wagner?

The mettle showed by African-American troops demonstrated that race was not a significant factor in a soldier's capability or courage.  Almost 300 of Shaw's troops were killed, including Shaw himself, and the South claimed a victory at the end of the day. Sill, the battle proved that African-American soldiers were just as brave and capable as white soldiers—and that became a symbolic victory for the Northern cause.  

the hereditary right of a monarch to rule from the mandate of heaven