I don't know how to analyze this quote from the book Americanah or what the meaning is behind it.

I don't know how to analyze this quote from the book Americanah or what the meaning is behind it. Also I don't understand how this quote relates to gender, classism or racism 

 "Dear non- American Black, when you make the choice to come to America, you become black. Stop arguing- stop saying I'm Jamaican or I'm Ghanaian. America doesn't care." Adichie. Americanah. Pg. 273)