On this day in 1862, a turning point for Grant and the Union:

U.S. Grant Captures Fort Donelson

Earns nickname "Unconditional Surrender"

Was this the most important battle of the Civil War?

Video summary

In response to Confederate commander Simon Boliver Bruckner's request for an armistice with terms, Grant responded:

"No terms except immediate and unconditional surrender can be accepted.  I propose to move immediately upon your works."