On October 1, 1838, Lord Auckland issued the Simla Manifesto, which stated that due to Dost Mohammed's dalliance with non-British interests, he was considered unfriendly, and would be removed from the throne of Afghanistan and replaced with Shah Shujah. Thus began a great misadventure, and one of the most humiliating defeats of the British. There was only one survivor of the Army of the Indus that had gone in to accomplish this action.

"When you're wounded and left,
On Afghanistan's plains,
And the women come out,
To cut up your remains,
Just roll on your rifle,
And blow out your brains,
And go to your Gawd,
Like a soldier."
Rudyard Kipling

Background: In June of 1838, Ranjit Singh, Shah Shujah and the British signed a secret agreement whereby Shah Shujah would relinquish his claim to Peshawar and in return be assisted in his desire to regain the throne of Afghanistan.
The Army of the Indus marched into Afghanistan in 1838, avoiding the Khyber Pass, as Ranjit Singh was unwilling to allow such a large force to pass through his domain.
On April 25th, 1839, the force arrived at Kandahar, Afghanistan's second largest city, where Shah Shujah was accepted, though somewhat grudgingly.
However, the Brits faced quite a different story at Ghazni, a hilltop fortress that had prepared for siege. Through the efforts of Henry Durand, Lieutenant of the Bengal Engineers (a British sapper), and intelligence given by Mohan Lal, a Kashmiri who had acquaintances on the inside, the British were able to take Ghazni with the loss of only 17 men.
The Brits left Ghazni on June 30, 1839 and arrived in Kabul in early July 1839. Kabul fell without a shot fired, but there was a cold reception for the invaders.
The Retreat from Kabul began on January 6th, 1842 and would in end an 'awful completeness' as the historian John Kaye said, barely a week later.
(more info to come, voters...this node's not quite finished)