The military failures of 1639 and 1640 occupy a central place in the most controversial century in British history. On the eve of the 1637 prayer book rebellion in Scotland Charles I was solvent, which was unusual for monarchs in the sixteenth and seventeenth centuries. His kingdoms enjoyed peace, also something of an anomaly during the period of the Thirty Years' War. And the furore of the 1620s was behind him, Parliament being no more than an unpleasant memory.

The King's decision to beat the drum of war in the cause of ecclesiastical uniformity made political stability impossible within Britain. England and Scotland certainly were not nations destined for political breakdown in the 1630s. Ireland, though not entirely pacified, had been tamed by Sir Thomas Wentworth, the Lord Deputy. The fateful decision to minimize religious diversity by force sparked division in all three realms. Neither Bishops' War caused civil war. But by demanding that some of his subjects take up arms to enforce royal policy upon another group of subjects, the King in effect invited referendum. The peace enforced by Charles's embarkation upon Personal Rule had been dictated by political considerations which were largely domestic. The King's war now sowed division, first between himself and his subjects, and by the end of 1640 (with the summoning of the Long Parliament), amongst his subjects as well.