Hazara and Pashtuns

Amir's best friend, Hassan, is a 'Hazara', whereas Amir is 'Pashtun' which seems to be a point made throughout the book.
But what are Hazara and Pashtun, and what is their history?

Hazara

Hazara are Persian speaking people who mainly live in central Afghanistan and Pakistan. They have Mongolian ancestry and are primarily Shi'a Muslims. However most people from Afghanistan are Sunni Muslims, and so the Hazara have been discriminated against for centuries.
Pashtun
The Pashtun are Afghanistan's largest ethnic group, and Pakistan's second largest. Most Pashtun's are Sunni Muslims, however a small minority are Shi'a.
The taliban are a group of severely right wing Pashtuns.

History
The Sunni and Shi'a Muslims have had a history of conflict. They are distinct ethnic groups and, as said before, the Hazara are a minority group in Afghanistan.
The battle of Uruzgan was between the Pashtun and the Hazara people. The Pashtuns pushed the Hazara out of Uruzgan and re-occupied it.
The two groups had different views on who should've been the successor when Mohammad died, and this is what split them and caused problems.