To Kill a King (2003)

The same story erupts in nearly every revolution. This one takes place in Britain during the reign of Charles I.

When Sir Thomas Fairfax leads an uprising against the king's troupes because of the tyranny Charles I imposes upon his people, Fairfax's faithful supporter puritan Oliver Cromwell becomes ever more zealous. The Parliament is easily bribed by the king and stronger measures are needed to "persuade" the king to yield more authority to the commons. Fairfax and Cromwell disagree on the method that ought to be utilized and they part on poor terms. Cromwell, who is played extraordinarily well by Tim Roth, seizes power and becomes as despotic as the king he beheads.

The film focuses on the relationship between Cromwell and Fairfax and keeps the audience more in the background of this well known story. The story isn't overly romanticized as the recent Elizabeth films are and it attempts to maintain an earthy and realist tone. 

The message is clear - diplomacy always yields better results than violence.

IMDB