The eastward advance had now gained possession of eighty miles of the Delagoa Bay railway, but the De Wet trouble and the disturbed state of the Western Transvaal made the continuation of the movement unsafe, and Lord Roberts called a halt. It was also advisable to wait until supplies had been collected at Middelburg, and until Buller, who was coming up from the south, was in a position to co-operate. Lord Roberts returned to Pretoria, leaving French in charge. Ian Hamilton, the emergency man, was sent to the west to deal with Delarey and De Wet. Towards the end of August Pole-Carew advanced to near Belfast, where he hoped soon to report himself to Buller.
Nearly three months had now elapsed since the battle of Diamond Hill. The progress of the Transvaal campaign was not very apparent, but it was real. Botha had been driven back along the Delagoa Bay railway, and neither the outbreaks in the Western Transvaal nor the meteoric incursion of De Wet had availed him. Nothing that had occurred elsewhere weakened the western advance to an extent that gave him an opportunity of effectively withstanding it. Buller was approaching, and Lord Roberts was no longer dependent upon one line of communication. The fugitive Free State Government had been driven into asylum with the fugitive Transvaal Government. No commandos were at large which could seriously threaten Bloemfontein, Johannesburg, or Pretoria; and the only organized body which the enemy could bring into the field was confronted by a British Army and had the barrier of the Portuguese frontier behind it. There was good hope that in a few weeks the already undermined fabric of Boerdom would totter to the ground, and that the worst that could happen was that some of the fragments might not fall clear of the British troops.
The arrival of Buller's force from the south gave Lord Roberts, who returned from Pretoria on August 25, the reinforcement justifying the resumption of the eastward advance. He found the troops unfavourably placed for immediate action. Botha was posted on each side of the railway near Belfast; the junction of his right with his left, which had different fronts, forming an obtuse salient angle. The greater part of the British force was south of the line and prevented by the nature of the ground from undertaking an enveloping movement on the enemy's left. Buller had kept the cavalry to heel, and it was lying compressed between him and Pole-Carew, who was entrenched round Belfast.
Lord Roberts' first act was to distribute over a wider front the conglomeration of troops, which were hampering each other's movements. French with his own cavalry, but without Buller's, was sent north of the line to face Botha's right flank and to clear Pole-Carew's left flank, while Buller worked up from the south towards the line.
The movement began on August 26, and by the afternoon French, having made a wide detour, had established himself north of Belfast; thus enabling Pole-Carew to leave the town and extend his division in front of the enemy's right. Buller's movement was at first directly northwards, on account of the soft ground. His march, like that of Pole-Carew on the other flank, was across the enemy's front, but neither of them was seriously checked and the casualties were few.
Buller had proposed to move eastward in the direction of Dalmanutha as soon as the ground permitted, but a cavalry reconnaissance discovered the enemy posted at Bergendal, close to the railway. The position was, in fact, the point of the obtuse angle formed by the two sections of the Boer front, one of which faced S.W. towards Buller, and the other west, towards Pole-Carew; and if it could be carried not only would Botha's line be broken, but Buller would be in a good position to deal with a retreat from either section,
The battle of Bergendal on August 27 was mainly a struggle between less than fourscore Transvaal Police and two battalions and forty guns of Buller's Division. The "Zarps" held a rocky ridge at the end of a spur, where they were bombarded for three hours, yet when the infantry advanced it was met with a vigorous rifle fire, which was continued almost without intermission until at last the kopje was carried by assault. The defence of the kopje was one of the most conspicuous feats of the war on the Boer side, and it is noteworthy that it was made by a body of regularly disciplined men. Owing partly no doubt to the difficulty of reinforcing such an isolated position, no effective support was given by Botha to the gallant little band, neither did he trouble Buller seriously with artillery fire; and the commandos east and north of the Zarps' kopje did little. He does not seem to have recognized that Bergendal was not a mere strong post, but the key of an unsound position which should at all hazards have been safeguarded. This Buller saw at once, and he moved so as to meet with the least interference from the enemy, who, having two fronts, could not act solidly upon either of them.
The capture of Bergendal dissolved the Boer position. The commandos facing Buller were driven off; and the right, which had been opposing French and Pole-Carew so feebly that neither of them suffered a single casualty, fell away. Buller went in pursuit, but was unable to worry the retreat. Some commandos withdrew eastwards along the line, others broke off towards Lydenburg and Barberton. The Boer Governments retired from Machadodorp to Nelspruit. Buller crossed the railway, and on August 29 Helvetia was taken. Next day the British prisoners of war, whom the Boers had brought away in the scuttle from Pretoria when Lord Roberts entered the city, were released at Noitgedacht by their captors, who were no longer in a position to detain them.
Botha had indeed been forced into retreat, but not cut off, and he escaped with all his guns and his losses were comparatively slight. His burghers were, as usual after a lost battle, demoralized and disheartened for the time being, but not, as was thought by the British Army, scared by their reverses into abject impotence. From the time of the occupation of Bloemfontein guerilla had been gradually taking the place of organized warfare, of which Bergendal was the last act, and which the burghers saw that they could not hope to wage successfully. The history of the previous seven months showed what could be won by guerilla, and what could be lost by pretending to be an Army. The fact that they were no longer able to act as a coherent military body did not permanently discourage them, and the struggle had not yet run more than one-third of its weary course.
It was, however, the general belief not only in Great Britain but also in the Army in South Africa, that the Boers had kicked their last kick at Bergendal. There might be a final wriggle or two; but the end was in sight, and before the first anniversary of the declaration of war, peace would again reign in the land. These not ill-founded hopes justified Lord Roberts' Proclamation of September 1, by which the Transvaal was formally incorporated in the British Empire.