Who faces the most discrimination?

ⒶⓁⓁⒾⓈⓄⓃ ★★★ • Never tell me the odds
So the other day, my Econ professor asked the class this question. "Who has faced discrimination the longest in our country (the United States)?" 
     
I immediately said "African Americans" because it's what I believe even if it wasn't the correct answer according to him. He quickly said no and someone next to me said "Native Americans" he said no. Then a small voice in the class said "women" and he said yes. 
  
So here is the question, who do you think faces the most descrimination?