Scotland, anxious for its own safety, hastened to sign the Covenant; and the Commons, "with uplifted hands," swore in St. Margaret's church to observe it. They pledged themselves to " bring the Churches of God in the three Kingdoms to the nearest conjunction and uniformity in religion, confession of faith, form of Church government, direction for worship and catechizing; that we, and our posterity after us, may as brethren live in faith and love, and the Lord may delight to live in the midst of us": to extirpate Popery, prelacy, superstition, schism, and profaneness; to " preserve the rights and privileges of the Parliament, and the liberties of the Kingdom;" to punish malig-nants and opponents of reformation in Church and State; to "unite the two Kingdoms in a firm peace and union to all posterity." The Covenant ended with a solemn acknowledgement of national sin, and a vow of reformation. "Our true, unfeigned purpose, desire, and endeavour for ourselves and all others under our power and charge, both in public and private, in all duties we owe to God and man, is to amend our lives, and each one to go before another in the example of a real reformation".
The conclusion of the Covenant had been the last work of Pym. A "Committee of the Two Kingdoms" which was entrusted after his death in December with the conduct of the war and of foreign affairs did their best to carry out the plans he had formed for the coming year. The vast scope of these plans bears witness to his amazing ability. Three strong armies, comprising a force of fifty thousand men, had been raised for the coming campaign. Essex, with the army of the centre, was charged with the duty of watching the king at Oxford. Waller, with another army, was to hold Prince Maurice in check in the west. The force of fourteen thousand men which had been raised by the zeal of the eastern counties, and in which Cromwell's name was becoming famous as a leader, was raised into a third army under Lord Manchester, ready to co-operate in Yorkshire with Sir Thomas Fairfax. With Alexander Leslie, Lord Leven, at its head, the Scotch army crossed the border in January "in a great frost and snow," and Newcastle was forced to hurry northward to arrest its march.
His departure freed the hands of Fairfax, who threw himself on the English troops from Ireland that had landed at Chester, and after cutting them to pieces marched as rapidly back to storm Selby. The danger in his rear called back Newcastle, who returned from confronting the Scots at Durham to throw himself into York, where he was besieged by Fairfax and by the Scotch army. The plans of Pym were now rapidly developed. While Manchester marched with the army of the Associated Counties to join the forces of Fairfax and Lord Leven under the walls of York, Waller and Essex gathered their troops round Oxford. Charles was thrown on the defensive. The troops from Ireland on which he counted had been cut to pieces by Fairfax or by Waller, and in North and South he seemed utterly overmatched. But he was far from despairing. He had already answered Newcastle's cry for aid by despatching Prince Rupert from Oxford to gather forces on the Welsh border; and the brilliant partizan, after breaking the sieges of Newark and Lathom House, burst over the Lancashire hills into Yorkshire, slipped by the Parliamentary army, and made his way untouched into York. But the success of this feat of arms tempted him to a fresh act of daring; he resolved on a decisive battle, and a discharge of musketry from the two armies as they faced each other on Marston Moor brought on, as evening gathered, a disorderly engagement.
On the one flank a charge of the King's horse broke that of the enemy; on the other, Cromwell's brigade won as complete a success over Rupert's troopers. " God made them as stubble to our swords," wrote the general at the close of the day; but in the heat of victory he called back his men from the chase to back Manchester in his attack on the royalist foot, and to rout their other wing of horse as it returned breathless from pursuing the Scots. Nowhere had the fighting been so fierce. A young Puritan who lay dying on the field told Cromwell as he bent over him that one thing lay on his spirit. "I asked him what it was," Cromwell wrote afterwards. "He told me it was that God had not suffered him to be any more the executioner of His enemies." At night-fall all was over; and the royalist cause in the north had perished at a blow. Newcastle fled over sea: York surrendered, and Rupert, with about six thousand horse at his back, rode southward to Oxford. The blow was the more terrible that it fell on Charles at a moment when his danger in the south was being changed into triumph by a series of brilliant and unexpected successes.
After a month's siege the King had escaped from Oxford followed by Essex and Waller; had waited till Essex marched to attack Prince Maurice at Lyme; and then, turning fiercely on Waller at Cropredy Bridge, had driven him back broken to London, two days before the battle of Marston Moor. Charles followed up his success by hurrying in the track of Essex, whom he hoped to crush between his own force and that under Maurice. By a fatal error, Essex plunged into Cornwall, where the country was hostile, and where the King hemmed him in among the hills, drew his lines tightly round his army, and forced the whole body of the foot to surrender at his mercy, while the horse cut their way through the besiegers, and Essex himself fled by sea to London. The day of the surrender was signalized by a royalist triumph in Scotland which promised to undo what Marston Moor had done. The Irish Catholics fulfilled their covenant with Charles by the landing of Irish soldiers in Argyle; and as had long since been arranged, Montrose, throwing himself into the Highlands, called the clans to arms.
Flinging his new force on that of the Covenanters at Tippermuir, he gained a victory which enabled him to occupy Perth, to sack Aberdeen, and to spread terror to Edinburgh The news fired Charles, as he came up from the west,to venture on a march upon London; but though the Scots were detained at Newcastle the rest of the victors at Marston Moor lay in his path at Newbury; and their force was strengthened by the soldiers who had surrendered in Cornwall, but who had been again brought into the field. The charges of the royalists failed to break the Parliamentary squadrons, and the soldiers of Essex wiped away the shame of their defeat by flinging themselves on the cannon they had lost, and bringing them back in triumph to their lines. Cromwell would have seized the moment of victory, but the darkness hindered his charging with his single brigade. Manchester, meanwhile, in spite of the prayers of his officers, refused to attack. Like Essex, he shrank from a crowning victory over the King. Charles was allowed to withdraw his army to Oxford, and even to reappear unchecked in the field of his defeat. The quarrel of Cromwell with Lord Manchester at Newbury was destined to give a new colour and direction to the war.