Why Are Mexican,Iraqi, and Black People Treated So Bad Here In U.S.A?

i was on my history cl and i've noticed those three races are so discriminated here in united states with black people being slaved and still there are black people being called things because of the color of skin and mexican people getting deported and seperating their family its just sad and iraqi people did damage our country but not all of them are bad theyre many nice iraqi people that dont mean harm...