Why is a self-employed professional called a “freelancer”?

The word freelance came out of the period between the fourteenth and sixteenth centuries, when mercenary knights with no particular allegiance would take their lances into battle for the prince or state that paid them the most money. They were referred to as freelancers by authors in the nineteenth century and operated much like the gunfighters in the American West. Now, a freelancer is anyone who works independently.