What's+the+origin+of+o.k

Nowadays this expression means everything is fine.**
 * The origin of the expression "o.k" comes from the North American Sucesion war and it means "0(zero) killed", every day the soldiers wrote in a blackboard the number of soldiers killed, when there weren´t any soldiers killed they wrote 0 (zero) and later the 0(zero) became o (letter).