The Second Civil War: military overview
Royalists, Scots and Presbyterians against the New Model Army
During the political wrangling that followed the inconclusive ending of the English Civil War, King Charles the First negotiated a secret treaty with the Scottish "Engager" faction, promising to impose Presbyterianism in England in exchange for a Scottish army to restore him to power.
During the spring of 1648, a number of pro-Royalist uprisings broke out around the country. In south Wales, garrison troops rebelled against the Parliamentarian government in London; northern Royalists seized Berwick and Carlisle; several towns were taken in Kent; the fleet mutinied and a squadron of warships defected to the King.
Fortunately for Parliament, the Engager invasion was badly coordinated with the uprisings in England and Wales. The New Model Army mobilized to suppress the insurrections before dealing with the Engagers. Cromwell marched against the Welsh insurgents while Fairfax secured London and advanced into Kent. Lambert went north to disrupt any Scottish advance into England.
A New Model detachment routed the Welsh insurgents at the battle of St Fagans in May 1648 then Cromwell's main force arrived to besiege their stronghold at Pembroke. Fairfax defeated the Kent Royalists at the battle of Maidstone and pursued the survivors into Essex where another Royalist uprising had broken out. The Essex Royalists fortified themselves at Colchester. Fairfax became bogged down in a long and bitter siege.
The Prince of Wales took command of the ships that had defected to the Royalists but he was forced to withdraw to the Netherlands by a Parliamentarian fleet under the Earl of Warwick. Pembroke surrendered in July 1648, allowing Cromwell to hurry north to join forces with Lambert. In August, Cromwell intercepted the Engagers at Preston and decisively defeated them during a three-day running battle. Colchester surrendered at the end of August, bringing the Second Civil War to an end.
The Army denounced King Charles for inflicting a second civil war upon the nation. Parliament was purged of the King's sympathisers and he was brought to trial as an enemy of the People. The King was pronounced guilty and executed in January 1649.
or move on to the next overview in the Military thread: the Third Civil War