What is the passage mainly concerned with?

Cola started out not as a soft drink but as a cure for headache back in the late 1800’s. John S. Pamberton, a druggist from Atlanta, had experimented for many months trying to find a cure for the common headache. He worked in his backyard, mixture and heating different combination of oils and flavors until he found one that seems promising. Pamberton bottled the mixture and began selling it in drugstores as a concentrated syrup that the customer had to mix with water before drinking. Cola’s transformation from a concentrated syrup to a carbonated soft drink came about quite by accident. One day, a customer came into a drugstore complaining of a headache and asked for a bottle of cola syrup. He wanted to take it right away. So he asked the clerk to mix the medicine while he waited. The clerk, instead of walking to the other end of the counter to get plain water, suggested mixing the syrup with soda water. The customer agreed, and after drinking it, remarked how good it tasted. The clerk continued offering the mixture and carbonated cola grew in popularity. Today carbonated colas are sold in most countries around the world. And although they no longer contain the ingredients to kill headaches, they are still very refreshing.