they are the people who either fought for parliament (round heads) or the king (royalists).
they called the round-heads 'roundheads' because they cut their hair!
they also called the royalists 'calivers' because they often rode Horses!
The Royalist side, or the Cavaliers, were the predominantly Catholic side.
As long as the King lived a Royalist threat would exist insisting on his return to the throne.
This is almost a serious answer: Their uniforms were much prettier ! But if you want to be on the winning side, more often then not then it's the drab but effective Parliamentary army.
There was no king in the american civil war, but of course America is not the only country on the planet, neither is it the only country to have a Civil War. In The English Civil War, supporters of King Charles I were "Royalists" or "Cavaliers; supporters of his opponent, Oliver Cromwell, were called "Roundheads."
It had to be protected against royalist counter revolution.
Charles was a royalist
Royalist
John Harris - Royalist - died in 1649.
John Harris - Royalist - was born in 1596.
Thomas Ingram - Royalist - died in 1672.
Thomas Ingram - Royalist - was born in 1614.
William Ashburnham - royalist - died in 1679.
John Coventry - Royalist - died in 1652.
David Jenkins - Royalist - was born in 1582.
David Jenkins - Royalist - died in 1663.
Thomas Gardiner - Royalist - died in 1662.
Thomas Gardiner - Royalist - was born in 1591.