The object of the invasion was unattainable by force, but something might be got by negotiation, if it was undertaken before force had definitely failed. They were losing heavily, by disease and want, while French recruits were pouring in. Therefore Dumouriez wished for time. The king's secretary had been captured, and he sent him with overtures, representing that the intended advance upon Paris was hopeless, and that Prussia had more interests in common with France than with Austria. Frederic William at once surrendered the original demands. He made no stipulations now regarding the future government of France or the treatment of the émigrés. He only demanded that Lewis should be restored, in such manner as might seem good to France, and that the propaganda of revolution should be put an end to. That propaganda was one of the weapons by which the French checked and embarrassed the champions of European absolutism, and it was obvious that it would receive encouragement from their success at Valmy. And it was a point of honour to speak for the imprisoned monarch. But it had become a vain thing. Dumouriez produced a newspaper with the decree of the new Assembly abolishing monarchy. It was hard to say what the allies were now doing on French soil. "Only do something for the king," said Brunswick, "and we will go." The Austrians would be satisfied if he was only a stadtholder. Kellermann promised that peace might be obtained if he was sent back to the Tuileries. It was all too late. The Prince, in whose behalf the allies invaded France, was now a hostage in the power of their enemies; all that they could obtain was a pledge not to carry the revolution into foreign countries. Their position grew more dangerous every day, and Dumouriez grew stronger.
At the end of September Frederic William abandoned Lewis to his fate. He had contributed to his dethronement by entering France, and he contributed to his execution by leaving it. He did not feel that he had deserved so prodigious a humiliation. If the Austrians had joined as they promised with 100,000 men, the march upon the capital would have been conceivable with energetic commanders. And the king could justly say that he had favoured spirited schemes, and had been baffled by the faltering commander-in-chief. He attempted, by throwing out hints of neutrality, to escape without further loss. Dumouriez calculated that every attack would weld the allies more closely together, and refrained from molesting them. Early in October they evacuated the conquered province, and retreated to the Rhine, pursued by a few random shots, while Dumouriez hastened to Paris, to be hailed as the saviour of his country.
The invasion of 1792 roused a crouching lion; and the French, after their easy and victorious defence, went over to the attack. Whilst the invaders were standing still, too weak to advance and too proud to withdraw, the conquest of Europe began. The king of Sardinia, as the father-in-law of the Comte d'Artois, had thrown himself into the counter-revolutionary policy, and the scheme for attacking Lyons. Of all European monarchs, since the murder of Gustavus, he was the most hostile. An army under Montesquieu occupied Savoy and Nice without resistance, and the people readily adopted the new system. A week later Custine seized the left bank of the Rhine, where diminutive secular and ecclesiastical territories, without cohesion, were an easy prey. The Declaration of Rights, said Gouverneur Morris, proved quite as effectual as the trumpets of Joshua. Mentz fell, October 21, and Custine occupied Frankfort and replenished his military chest. This excursion into the middle of the Empire was not authorised by State policy. The idea was already taking shape that the safety of France required the defensible and historic, or, as they unscientifically called it, the natural frontier of the Rhine, and that the grand conflict with Austria should be transferred to Italy. Germany was a nation of armed men, and was best let alone. In Italy, the Austrians would have only their own resources for war. Their most vulnerable point was the outlying principality of Belgium, so distant from Vienna and so near to Paris.
Dumouriez was now at liberty to deliver the stroke by which he had hoped to stop the invasion, as Scipio drove Hannibal from Italy by landing in Africa. By carrying the war in that direction he would occupy the Imperialists, and would not excite the resentment of Prussia. The country had not long been pacified, and it presented the unusual feature that Conservatives and Liberals alike were patriotic and rebellious. As a place where disaffection would assist war, it was there that the process of European revolution would properly begin. On October 19 Dumouriez assumed the command of 70,000 men, in the region he had held before his flank march to the Argonne. One of his lieutenants was the Peruvian adventurer Miranda, whose mission it was to apply the movement in Europe to the rescue of Spanish America. The other was known as Prince Égalité, senior, whose wonderful future was already foreseen both by Dumouriez and Danton.
During the operations in Champagne the Austrians had begun the siege of Lille, and at the turning of the tide they withdrew across the frontier, and took up a strong position at Jemmapes, in front of Mons, with 13,000 men. Clerfayt, again, was at their head; and when, on November 6, he saw the French army approaching, nearly 40,000 strong, like Nelson in the hour of death he appeared in all his stars and gold lace, that his men, seeing him, might take heart. He was defeated, and the next evening, at the theatre of Mons, Dumouriez was acclaimed by the Flemish patriots. A week later he was at Brussels, and before the end of the month he was master of Belgium. Holland was undefended, and he proposed to conquer it; but Antwerp was already in the power of the French, and his government feared that England would come to the defence of the Dutch. They directed him to march upon Cologne and complete the conquest of the Rhine.
By a decree of November 19 the Convention proffered sympathy and succour to every people that struck a blow for freedom; but the cloven hoof of annexation soon appeared, and it was avowed that the war would be carried on, that the financial needs of France might be supplied, at the expense of the populations which the French arms delivered. These things offended the political, if not the moral sense of Dumouriez. He became alienated from the Convention; and as England went to war on the death of the king, there was no consideration of policy protecting Holland. The invasion was undertaken, and immediately failed. The Austrians, under the duke of Coburg, who on that day founded the great fortunes of his house, came back in force, and gave battle at Neerwinden, close to the fields of Landen and of Ramillies. Here, March 18, Clerfayt crushed Dumouriez's left wing, and recovered the Belgic provinces as suddenly as he had lost them four months earlier.
Dumouriez had already resolved to treat with the Imperialists for common action against the Regicides. Five days after his defeat he informed Coburg that, with his support, he would lead his army against Paris, disperse the Convention, and establish a constitutional monarchy without the émigrés. He promised that the better part of his force would follow him. The volunteers were Jacobinical; but the regulars were jealous of the volunteers, and would obey their general. As he felt his way, hostile officers watched him, and reported what was going on in the camp of the new Wallenstein. Twice the Jacobins attempted to avert the peril. They invited Dumouriez to Paris, that he might place himself at their head and overpower the Girondin majority, and they employed men to assassinate him. At last they sent the minister of war, accompanied by four deputies, to arrest him. There was to have been a fifth, but he did not arrive in time, and his absence saved France. For Dumouriez seized the envoys of the Convention, and handed them over to Coburg, to be hostages for the life of the queen. The deputy who failed to appear was Carnot. After that, Dumouriez was deserted by his men, and fled to the Austrian camp. He survived for thirty years. He became one of the shrewdest observers of Napoleon's career, and was the confidential correspondent of Wellington on the art they understood so well. The future "king of the French," who went over with him, remained true to his chief during the strange vicissitudes of their lives; and at the Restoration he asked that he should be made a marshal. "How could you think," was the proud comment of Dumouriez, "that they have forgotten the Argonne?"
On the 20th of June in the following year Louis Philippe drove into town from Twickenham to learn the news from the Low Countries. His sons still know the spot where he found his old commander gesticulating on the pavement at Hammersmith, and learned from him how the great war, which began with their victory at Valmy, had ended under Napoleon at Waterloo.