The declaration of war was a mistake. Persia had already taken the alarm, and raised the siege of Herat. Dost Mohammed Khan may have been a usurper, but he had been accepted by the Afghan people as their ruler, and he was a man of undoubted capacity. If he had been properly treated in 1836-37 he might have become as useful an ally to the British government as he proved himself to be twenty years later. Shah Shuja, on the other hand, whom the British wished to set up in his room, was a weak and worthless prince, and it was doubtful at the time whether the Afghan people would accept him as their ruler, especially if he were forced upon them by the British government. [Sidenote: First Afghan war, 1838-42.] Thus began the first Cabul war. The British army was shut out from the Punjab by Runjeet Singh, and compelled to take a circuitous route through Sind. A bridge of boats was constructed to carry the army over the Indus at Sukkur; but in those days Sind was a foreign territory, and no reliance could be placed on its rulers. Indeed, had the British met with a defeat in Afghanistan, the Amirs, or rulers of Sind, would possibly have destroyed the bridge, and cut off their return to India. [Sidenote: British advance to Cabul, 1839.] In February, 1839, the British army crossed the river Indus, and advanced along the Bolan Pass to Quetta, and thence to Candahar. Major Rawlinson remained at Candahar as minister and envoy of Shah Shuja, supported by a force under the command of General Nott. The main army, under Sir John Keane, advanced northward, captured the important fortress of Ghazni, and conducted Shah Shuja to Cabul, whilst Dost Mohammed Khan fled away northward to Bokhara. Shah Shuja was placed on the throne of Afghanistan, under the guidance of Sir William Macnaghten, the minister and envoy at Cabul, protected by the British army under Keane, who was subsequently created Baron Keane of Ghazni.[25] [Sidenote: British successes, 1840.]