Battle of Naseby was part of the First English Civil War, a conflict between King Charles I and the Parliament forces over the political structure of the country - king was trying to keep his prerogatives while the Parliament was trying to introduce constitutional monarchy.
After the Royalists have taken the Parliamentarian stronghold of Leicester the forces of King Charles I were moving north for recovery. Sir Thomas Fairfax has retreated his units from siege of Oxford in order to attack the King’s army. The king pursued by Fairfax decided to face him in the battle near Naseby.
Despite the advantage of the Parliamentarians the battle was tough, but King Charles I lost almost all of his army - out of 7400 men 1000 was killed and over 5000 captured. This was the last battle in which Royalists were able to set up a strong army during First English Civil War.
Oliver Cromwell becomes a leader of revolt against the unjust reign of King Charles I, the civil war that changed the England forever.