They are the descendants of the Mongol hordes, who invaded through Afghanistan. There has been some intermarriage, but they they are largely ethnically distinct to this day.
The word “Hazara” literally means “thousand”, which was a standard Mongol military unit.
Around Bamiyan (where the ancient cliff-side Buddha statues were destroyed by the Taliban), Afghan fighters killed one of Mongol Princes. In retribution, the Khan ordered that the entire population be exterminated. To this day, the area around Bamiyan is almost all Hazara. They have East Asian eye folds, and still play the unique Mongol style of wrestling.
There is a long history of discrimination against Hazara in Afghanistan - partly ethnic, and partly religious, as the Hazara are mostly of the minority Shia sect. Both forms of discrimination were passionate, rather than half-hearted.
The Taliban is largely a movement of the Pashtun ethnicity in Afghanistan, who made up around 40% of the population, but has dominated politically (the royal family were Pashtun). When the Taliban were taking over Afghanistan, they promoted ethnic cleansing of other groups, famously calling for “Uzbeks to Uzbekistan, Tajiks to Tajikistan, and Hazara to Ghoristan (the land of the dead - the graveyard).
After the American invasion, the improvement in education and career prospects for Hazara increased dramatically. Even integration has improved somewhat, such as inclusion on TV programs - but bigotry is still not hard to find.
Thank you or the informative synopsis.