The state of the contending parties, from the battle of Edge Hill, for nearly two years, was very singular and very complicated. The king remained at Oxford, distracted by opposing counsels, and perplexed by various difficulties. The head-quarters of his enemies, at London, were no less the seat of intrigues and party animosities. The Presbyterians were the most powerful, and were nearly as distrustful of the Independents as they were of the king, and feared a victory over the king nearly as much as they did a defeat by him, and the dissensions among the various sects and leaders were no secret in the royalist camp, and doubtless encouraged Charles in his endless intrigues and dissimulations. But he was not equal to decisive measures, and without them, in revolutionary times, any party must be ruined. While he was meditating and scheming, he heard the news of an alliance between Scotland and the parliament, in which the Presbyterian interest was in the ascendency. This was the first great blow he received since the commencement of the war, and the united forces of his enemies now resolved upon more vigorous measures.
At the opening of the campaign, the parliament had five armies--that of the Scots, of twenty-one thousand; that of Essex, ten thousand five hundred; that of Waller, five thousand one hundred; that of Manchester, fourteen thousand; and that of Fairfax, five thousand five hundred--in all, about fifty-six thousand men, of whom the committee of the two kingdoms had the entire disposal. In May, Essex and Waller invested Oxford, while Fairfax, Manchester, and the Scots met under the walls of York. Thus these two great royalist cities were attacked at once by all the forces of parliament. Charles, invested by a stronger force, and being deprived of the assistance of the princes, Rupert and Maurice, his nephews, who were absent on their marauding expeditions, escaped from Oxford, and proceeded towards Exeter. In the mean time, he ordered Prince Rupert to advance to the relief of York, which was defended by the marquis of Newcastle. The united royalist army now amounted to twenty-six thousand men, with a numerous and well appointed cavalry; and this great force obliged the armies of the parliament to raise the siege of York. Had Rupert been contented with this success, and intrenched himself in the strongest city of the north of England, he and Newcastle might have maintained their ground; but Rupert, against the advice of Newcastle, resolved on an engagement with the parliamentary generals, who had retreated to Marston Moor, on the banks of the Ouse, five miles from the city.