For various reasons, 1645 must be regarded as the fulcrum year of the First Civil War. Defeat at Marston notwithstanding, the Royalists had recorded major victories in Scotland, and Charles still commanded widespread loyalty.
Parliament had won decisively at Marston Moor but had failed to capitalise on this success, and the New Model Army was untested. All was still to play for in early 1645.
However, the New Year brought Charles a string of setbacks. In April, Cromwell severed the lines of communication between Charles in Oxford and Rupert in Wales, and when Royalist scouts stumbled across Parliamentary troops on the outskirts of Daventry, Charles made the fateful decision to engage them in battle.
Naseby is the second great battle of the First Civil War, and a further illustration of the importance of the cavalry in determining the outcome of battles. As at Edgehill, the Royalists advanced too far and left their infantry undefended as they looted baggage trains. The well-organised Ironsides made no such mistakes and cut down their opponents with a series of decisive, disciplined charges. With 1000 dead and 5000 captured, Naseby was another major Royalist disaster.
News from the West Country was no more encouraging. Immediately after Naseby, Rupert moved west to shore up crumbling Royalist positions and make a decisive stand in Bristol. However, plague swept through the town, decimating Rupert's troops and he was forced to surrender. An outraged Charles then dismissed his nephew from his service.
The news from Scotland was even worse. Montrose's 'year of miracles' finally ended in September 1645 when he was finally run to earth at Philiphaugh on the Yarrow and decisively beaten. Montrose evaded capture but the victorious Covenanters slaughtered their captives. By late 1645, Royalism was dead as a military force and only a political solution could save Charles.
Naseby was the second truly decisive battle of the First Civil War and a disaster for the Royalists - approximately 5000 Royalist troops were taken prisioner. At one point in the battle, Charles attempted to personally lead his troops into battle, and only the timely intervention of the Earl of Carnwath prevented him from doing so.