Lewes and Evesham bookend Simon's brief period as the power broker of England. Lewes takes place in 1264 and pits Simon with the support from many prominant barons against Henry III and his royalist faction. His victory and imprisonment of Henry made him king in all but name. Evesham, fought one year later, finds Simon weakened by the treachery of his own barons, facing the much more dangerous Prince Edward. It would be Simon's last battle.

The system provides a unique simulation of 13th Century warfare. With only 12 pages of rules plus commentary, the game plays fast and furiously. Each player must preplan the order for his Battles with the use of Command Points. This system has built in limitations on leaders and troops, fog of war, and the chaos of the medieval battlefield. More importantly, it does this by employing a simple, elegant mechanic and not struggle with the rulebook.

The game turn is interactive, where players must commit the orders of there battles to seize the initiative and go on the attack, or hold back on defence. Players must carefully time when to commit to action the plans that they have made. Or, should things go badly, they will be forced to make the difficult choice of when to change their plans and react. And be forewarned, the cavalry of the era is impetuous; the movement of enemy troops may trigger a mad charge for glory that neither player expects.

Rules also cover individual unit morale, battle morale, cohesion, ranged fire, melee, and leadership, including special rules for Prince Edward and his Battle. Both the battles of Lewes and Evesham are covered in historical as well as "what if" scenarios. Barons' War is fast paced, playable in under 3 hours with high scenario replayability.