The kings or their ambassadors had been quarrelling at Vienna, where they had met to arrange the affairs of Europe; but the news of Napoleon's return made them agree. All promised to help in resisting him, and it was settled that in six weeks 700,000 men should be ready to fight. As a matter of fact, nothing of the kind was done. England, indeed, sent an army over into Belgium, but it was not a large one, for there were only 30,000 British troops in it, and some of these were new recruits. Wellington was, of course, put in command, but the veteran soldiers whom he had led to victory in Portugal and Spain were, for the most part, in America, whither they had been sent for the war with the United States. The total number that he had was rather above 100,000, and this was made up by Germans, who, for the most part, were good troops; Dutch, who were not so good, but still fair; and Belgians, many of whom were very bad. The Prussians had an army of about 80,000 in the field, under Marshal Blucher, their most famous general. Napoleon, on the other hand, had an army of 130,000, composed, for the most part, of excellent soldiers, the veterans whom he had commanded in so many wars. He hurried from Paris, which he left on June 12, to the French frontier. His plan was to attack first the Prussians and then the English with his whole force. Wellington was at Brussels, Blucher at Namur, that is about fifty miles apart. On June 16 Napoleon attacked the Prussians' left at Fleurus and defeated them, but not so heavily as to make them unable to move. On the same day one of his marshals, Ney, fell on the British troops at Quatre Bras. He did not begin his attack till late in the day; had he been earlier, he might have done more, for he would certainly have found his adversaries weaker. As it was, though some Belgian troops fled from the field, and the Duke of Brunswick's legion was broken for a time, their leader being killed, Ney could not drive the British from their position. The total loss of the Allies was about 25,000 men in killed, wounded, and prisoners; that of the French about 16,000. Napoleon had won a victory, but not so great a one as he wanted. He had beaten, but not routed, the Prussians, and he had not beaten the British at all.

On the 17th there was no fighting; it was on the 18th that the great battle was fought which was to put an end to Napoleon's power. Wellington's line of battle was along a ridge about two miles long. Behind it was the Forest of Soignies, into which he could retreat if it became necessary. In front of him on the right was a country house called Hougoumont, and about the centre a farm named La Haye Sainte. The ridge gave some shelter to his troops from the French cannon. He had about 62,000 men, with 156 guns; Napoleon had 65,000 with 246 guns; but some of Wellington's troops were, as has been said, worth but very little. It was not so much that they wanted courage, but they were better disposed to the French than to us.

Napoleon did not begin the attack until about half-an-hour before noon. There had been rain in the night, and it would be convenient that the ground should dry before he moved. Still, as it turned out, this was a mistake. Napoleon did not know that the Prussians were as near the English army as they really were; if he had, he would certainly have done his best to beat the British troops before they could possibly come up. The first thing done was to attack Hougoumont. Here fierce fighting went on during the whole day, but the French never got possession of the whole place. The house was always held by the British garrison. But at the centre things were somewhat better for the French. They took the farmhouse of La Haye Sainte, and routed the Dutch-Belgian brigade. Yet here, too, they suffered a considerable loss; thrown into disorder by the heavy fire from the English lines, they were charged by the Union Brigade of cavalry on one side, and by the Household Brigade or Lifeguards on the other. Napoleon, who had found out from a Prussian officer who had been taken prisoner that Blucher was advancing, made more and more furious efforts to break the English line. A huge body of cavalry, as many as 12,000 in number, charged time after time, but could not break the squares of British infantry. "I shall beat them yet," Wellington said about this time to one of his officers. Still, the battle was far from being won. The fierce cannonade had so thinned a part of the line where the Hanoverians were posted that the Duke himself had to rally the wavering troops.

It was now late. Napoleon had been vainly trying for eight hours to overcome the stubborn British lines, and now the Prussians had appeared on the field. He made one last effort, sending the last ten battalions of the Old Guard. It was in vain. They charged in two columns, but both were broken and driven back. Then Wellington ordered an advance of the whole British line. The French army broke up in hopeless confusion and fled. Napoleon's Empire had fallen. It was a splendid victory, but dearly bought. The British loss in killed and wounded was 15,000, the Prussians nearly half as much. This last fact shows that the Prussian army had a much greater share in the battle than most people think.