Chicory has been used as a coffee extender, especially in the deep south when supplies of coffee were scarce. New Orleans is noted for their chicory coffee.
chicory is mixed in with the coffee beans. I believe it is to take some of the bitterness out of the coffee. I believe it is a New Orleans thing mostly.
Yes it was added to coffee all over the world to make the coffee less bitter and to ameliorate the effects of caffeine.
When coffee was first introduced to the west (about 600years ago) it had a deleterious effect on people as would ephedrine today. I know that is hard to believe but is true never the less.
Chicory was added to reduce these effects and to improve the taste.