In the early summer of 1672, when William resolved to concentrate all his available forces for the defence of Holland covered by its water-line, the military situation was apparently hopeless. Had Turenne and Luxemburg made a united effort to force this line at the opening of the campaign the probability is that they would have succeeded. Instead of doing so they expended their energies in the capture of a number of fortified places in Gelderland, Overyssel and North Brabant; and in the meantime the stadholder was week by week strengthening the weak points in his defences, encouraging his men, personally supervising every detail and setting an example of unshaken courage and of ceaseless industry. He had at his side, as his field-marshal, George Frederick, Count of Waldeck, an officer of experience and skill who had entered the Republic's service, and Van Beverningh as Commissioner of the States-General. With their help and counsel he had before autumn an efficient army of 57,000 men on guard behind entrenchments at all assailable points, while armed vessels patrolled the waterways. Outside the line Nijmwegen, Grave, Coevorden, Steenwijk and other smaller places had fallen; but the Muenster-Cologne forces, after a siege lasting from July 9 to August 28, had to retire from Groningen. The French armies were all this time being constantly weakened by having to place garrisons in the conquered provinces; and neither Turenne nor Luxemburg felt strong enough to attack the strongly-protected Dutch frontiers behind the water-line.

The prince, however, was not content with inaction. Assuming the offensive, he ventured on a series of attacks on Naarden and on Woerden, raised the siege of Maestricht, and finally made an attempt to cut the French communications by a march upon Charleroi. All these raids were more or less failures, since in each case William had to retreat without effecting anything of importance. Nevertheless the enterprise shown by the young general had the double effect of heartening his own troops and of undermining the overweening confidence of the enemy. A hard frost in December enabled Luxemburg to penetrate into Holland, but a rapid thaw compelled a hasty withdrawal. The only road open to him was blocked by a fortified post at Nieuwerbrug, but Colonel Vin et Pain, who was in command of the Dutch force, retired to Gouda and left the French a free passage, to the stadholder's great indignation. The colonel was tried on the charge of deserting his post, and shot.

The year 1673 was marked by a decisive change for the better in the position of the States. Alarm at the rapid growth of the French power brought at last both Spanish and Austrian assistance to the hard-pressed Netherlands; and the courage and skill of De Ruyter held successfully at bay the united fleets of England and France, and effectually prevented the landing of an army on the Dutch coast. Never did De Ruyter exhibit higher qualities of leadership than in the naval campaign of 1673. His fleet was greatly inferior in numbers to the combined Anglo-French fleet under Prince Rupert and D'Estrees. A stubborn action took place near the mouth of the Scheldt on June 7, in which the English had little assistance from the French squadron and finally retired to the estuary of the Thames. Another fierce fight at Kijkduin on August 21 was still more to the advantage of the Dutch. Meanwhile on land the French had scored a real success by the capture of the great fortress of Maestricht with its garrison of 6000 men, after a siege which lasted from June 6 to July 1. All attempts, however, to pass the water-line and enter Holland met with failure; and, as the summer drew to its close, the advance of Imperial and Spanish forces began to render the position of the French precarious. William seized his opportunity in September to capture Naarden before Luxemburg could advance to its relief. He then took a bolder step. In October, at the head of an army of 25,000 men, of whom 15,000 were Spanish, he marched to Cologne and, after effecting a junction with the Imperial army, laid siege to Bonn, which surrendered on November 15. This brilliant stroke had great results. The French, fearing that their communications might be cut, withdrew from the Dutch frontier; and at the same time the Muenster-Cologne forces hastily evacuated the eastern provinces. The stadholder before the end of the year entirely freed the country from its invaders. Once more a Prince of Orange had saved the Dutch Republic in its extremity.

The effect of this was to place almost supreme power in his hands. Had the prince at this moment set his heart upon obtaining the title of sovereign, he would have had but little difficulty in gratifying his ambition. Leading statesmen like the Council-Pensionary Fagel, the experienced Van Beverningh, and Valckenier, the most influential man in Amsterdam, would have supported him. But William was thoroughly practical. The freeing of the Provinces from the presence of the enemy was but the beginning of the task which he had already set before himself as his life-work, i.e. the overthrow of the menacing predominance of the French power under Louis XIV. His first care was the restoration of the well-nigh ruined land. The country outside the water-line had been cruelly devastated by the invaders, and then impoverished by having for a year and a half to maintain the armies of occupation. Large tracts on the borders of Holland, Utrecht and Friesland, submerged by the sea-waters through the cutting of the dams, had been rendered valueless for some years to come, while those parts of Holland and Zeeland on which the enemy had not set foot had been crushed beneath heavy taxes and the loss of commerce.