After Charles II's father, Charles I, was executed during the English Civil War, England became a republic for a few years under the leadership (and widely known as a dictatorship) of Oliver Cromwell. This harsh rule lasted about 7 years, and, after Cromwell died (and his son failed at taking his place), political instability led to the restoration of the monarchy, with Charles II taking the throne. He was then known as the "Merry Monarch" because 1) of the relief of the dictatorship of Cromwell being over and 2) he was willing to consent to Parliament's wishes in fear of another revolution.
I think we have two different holidays for them because they honor 2 different events in history .
