Step 1 : Introduction to the question "What are the two main ingredients in a Cuba Libre?"
...Cuba experienced a "free Cuba" movement after the end of the Spanish-American War. Most believe this is the time when the Cuba Libre was first made. The original Cuba Libre called for squeezing the juice of a whole lime into the glass before the addition of the rum. There should be ice in the glass, of course. Add the amount of rum to taste. Then top the drink off with Coke. This isn't the sticky-sweet party drink Rum and Coke. The lime adds a degree of tartness to cut the sweetness of the Coke. Source: SeriousEats.com