Cromwell had shown his capacity for organization in the creation of his regiment; his military genius had displayed itself at Marston Moor. Newbury first raised him into a political leader. " Without a more speedy, vigorous, and effective prosecution of the war," he said to the Commons after his quarrel with Manchester, "casting off all lingering proceedings, like those of soldiers of fortune beyond sea to spin out a war, we shall make the kingdom weary of us, and hate the name of a Parliament." But under the leaders who at present conducted it a vigorous conduct of the war was hopeless. They were, in Cromwell's plain words, " afraid to conquer." They desired not to crush Charles, but to force him back, with as much of his old strength remaining as might be, to the position of a constitutional King. The old loyalty, too, clogged their enterprise; they shrank from the taint of treason. "If the King be beaten," Manchester urged at Newbury, "he will still be king; if he beat us he will hang us all for traitors." To a mood like this Cromwell's attitude seemed horrible: "If I met the King in battle," he answered, according to a later story, " I would fire my pistol at the King as at another." The army, too, as he long ago urged at Edge-hill, was not an army to conquer with.

Now, as then, he urged that till the whole force was new modelled, and placed under a strictet discipline, "they must not expect any notable success in anything they went about." But the first step in such a re-organization must be a change of officers. The army was led and officered by members of the two Houses, and the Self-denying Ordinance, as it was introduced by Cromwell and Vane, declared the tenure of military or civil offices incompatible with a seat in either. The long and bitter resistance which this measure met before it was finally passed in a modified form was justified at a later time by the political results which followed the rupture of the tie which had hitherto bound the army to the Parliament. But the drift of public opinion was too strong to be withstood. The passage of the Ordinance brought about the retirement of Essex, Manchester, and Waller; and the new organization of the army went rapidly on under a new commander-in-chief, Sir Thomas Fairfax, the hero of the long contest in Yorkshire, and who had been raised into fame by his victory at Nantwich, and his bravery at Marston Moor. But behind Fairfax stood Cromwell; and the principles on which Cromwell had formed his brigade were carried out on a larger scale in the "New Model." The one aim was to get together twenty thousand "honest" men. "Be careful," Cromwell had written, " what captains of horse you choose, what men be mounted.

A few honest men are better than numbers. If you choose godly honest men to be captains of horse, honest men will follow them." The result was a curious medley of men of different ranks among the officers of the New Model. The bulk of those in high command remained men of noble or gentle blood, Montagues, Pickerings, Fortescucs, Sheffields, Sidneys, and the like. But side by side with these, though in far smaller proportion, were seen officers like Ewer, who had been a serving-man, like Okey, who had been a drayman, or Rainsborough, who had been a "skipper at sea." A result hardly less notable was the youth of the officers. Among those in high command there were few who, like Cromwell, had passed middle age. Fairfax was but thirty-three, and most of his colonels were even younger. Equally strange was the mixture of religions in its ranks; though a large proportion of the infantry was composed of pressed recruits, the cavalry was for the most part strongly Puritan, and in that part of the army especially dissidence of every type had gained a firm foothold.

Of the political and religious aspect of the New Model we shall have to speak at a later time; as yet its energy was directed solely to " the speedy and vigorous prosecution of the war." Fairfax was no sooner ready for action than the policy of Cromwell was aided by the policy of the King. From the hour when Newbury marked the breach between the peace and war parties in the Parliament, the Scotch Commissioners and the bulk of the Commons had seen that their one chance of hindering what they looked on as revolution in Church and State lay in pressing for fresh negotiations with Charles. Commissioners met at Uxbridge to draw up a treaty; but the hopes of concession which Charles held out were suddenly withdrawn in the spring. He saw, as he thought, the Parliamentary army dissolved and ruined by its new modelling, at an instant when news came from Scotland of fresh successes on the part of Montrose, and of his overthrow of the Marquis of Argyle's troops in the victory of Inverlochy. "Before the end of the summer," wrote the conqueror, "I shall be in a position to come to your Majesty's aid with a brave army." The party of war gained the ascendant; and in May the King opened his campaign by a march to the north.

Leicester was stormed, the blockade of Chester raised, and the eastern counties threatened, until Fairfax, who had been unwillingly engaged in a siege of Oxford, hurried at last on his track. Cromwell, who had been suffered by the House to retain his command for a few days in spite of the Ordinance, joined Fairfax as he drew near the King, and his arrival was greeted by loud shouts of welcome from the troops. The two armies met near Naseby, to the north-west of Northampton. The King was eager to fight. " Never have my affairs been in as good a state," he cried; and Prince Rupert was as impatient as his uncle. On the other side, even Cromwell doubted as a soldier the success of the newly-drilled troops, though religious enthusiasm swept away doubt in the assurance of victory. " I can say this of Naseby," he wrote soon after, " that when I saw the enemy draw up and march in gallant order towards us, and we a company of poor ignorant men, to seek to order our battle, the general having commanded me to order all the horse, I could not, riding alone about my business, but smile out to God in praises, in assurance of victory, because God would by things that are not bring to nought things that are.

Of which I had great assurance, and God did it." The battle began with a furious charge of Rupert uphill, which routed the wing opposed to him under Ireton; while the royalist foot, after a single discharge, clubbed their muskets and fell on the centre under Fairfax so hotly that it slowly and stubbornly gave way. But Cromwell's brigade were conquerors on the left. A single charge broke the northern horse under Langdale, who had already fled before them at Marston Moor; and holding his troops firmly in hand, Cromwell fell with them on the flank of the royalist foot in the very crisis of its success. A panic of the King's reserve, and its flight from the field, aided his efforts: it was in vain that Rupert returned with forces exhausted by pursuit, that Charles, in a passion of despair, called on his troopers for "one charge more." The battle was over: artillery, baggage, even the royal papers, fell into the conquerors' hands; five thousand men surrendered; only two thousand followed the King in his headlong flight from the field. The war was ended at a blow.

While Charles wandered helplessly along the Welsh border in search of fresh forces, Fairfax marched rapidly into Somersetshire, and routed the royal forces at Langport. A victory at Kilsyth, which gave Scotland for the moment to Montrose, threw a transient gleam over the darkening fortunes of his master's cause; but the surrender of Bristol to the Parliamentary army, and the dispersion of the last force Charles could collect in an attempt to relieve Chester, was followed by news of the crushing and irretrievable defeat of the "Great Marquis " at Philip-haugh. In the wreck of the royal cause we may pause for a moment over an incident which brings out in relief the best temper of both sides. Cromwell "spent much time with God in prayer before the storm " of Basing House, where the Marquis of Winchester had held stoutly out through the war for the King. The storm ended its resistance, and the brave old royalist was brought in a prisoner with his house flaming around him. He "broke out," reports a Puritan bystander, "and said, 'that if the King had no more ground in England but Basing House he would adventure it as he did, and so maintain it to the uttermost,' comforting himself in this matter! that Basing House was called Loyalty." Of loyalty such as this Charles was utterly unworthy.

The seizure of his papers at Naseby had hardly disclosed his earlier intrigues with the Irish Catholics when the Parliament was able to reveal to England a fresh treaty with them, which purchased no longer their neutrality, but their aid, by the simple concession of every demand they had made. The shame was without profit, for whatever aid Ireland might have given came too late to be of service. The spring of 1646 saw the few troops who still clung to Charles surrounded and routed at Stow. "You have done your work now," their leader, Sir Jacob Astley, said bitterly to his conquerors, " and may go to play, unless you fall out among yourselves".