My history of the region is a bit vague, but I was under the impression that the Wahhabi were mostly restricted to the Arabian peninsula, where (with the Saudis) they waged near-constant war against the Ottomans (eventually being defeated by Mehmet Ali), and other Arabian tribes (losing to the Rashidis) before finally getting their way in the early of the 20th Century.
How and when did they spread to Afghanistan?
The Egyptians defeated the Wahhabi in battle in 1815, and finally defeated their final stronghold of Riyadh in 1818, but in about 1821 they were beginning to reemerge under the leadership of Turki Ibn Saud.
Several notable figures brought Wahhabi, in various forms, into the Pathan territories and India.
The earliest was Ghulam Rasul, who was studying the Hadith in Arabia shortly after the turn of the 19th Century, in the Wahhabi heartland. When he returned to Benares he began preaching a radical version of Islam that offended Muslims in India - Wahhabi.
Another - a Bengali named Shariatullah - was living in the Hijaz (the region of Arabia containing the holy cities) at the same time, and was there when the Wahhabi took Mecca in 1805. He only left Arabia after the fall of Riyadh in 1818. When he returned to Bengali he preached a diluted version of Wahhabi.
Most significant was Syed Ahmed who arrived in Arabia on the hajj (pilgrimage) with about 400 followers in about 1821. This was after the fall of Riyadh, but during a time when the Wahhabi were rebuilding. He remained for a few years and eventually returned to India in about 1821 finding the region of Hindustan now firmly under British rule. His Islamic preachings quickly found favour with local Muslims and he soon created a jihad movement and traveled into Afghanistan.
His teaching was that British rule of India had turned it into "Dar ul-Harb" (Domain of Enmity") and that he and his Wahhabis would establish a "Dar ul-Islam" (Domain of Islam) in Afghanistan and use it to unleash jihad upon Dar ul-Harb", reflecting the Prophet's movement from Mecca to Medina. Jihad can only be launched from Dar ul-Islam hence their movement into Afghanistan. They lauched their jihad against the Sikhs which was initially successful, but then crushed. A decade later the movement was revived, and another unsuccessful campaign was launched out of Afghanistan. Finally a third movement established itself in a much more sophisticated and covert way in India, building complex networks across the country and using code to communicate. A sophisticated propaganda machine was put in place. This movement took part (and was crucial in creating) the Sepoy Mutiny of 1857. The British identified the Wahhabi as the central figures in the Mutiny, such that in Delhi they were executed on sight, and virtually all Muslims were killed.
If anyone needs any evidence that Radical Islam is a sickness that needs to be eradicated immediately, here it is.
