Why are blacks called african american....?

while whites Latino`s and asians are just called american? im not being racist so please no rude answers i just wanna know because one of my best friends is black and she has NEVER been to africa so..im just curious so if blacks are called african american shouldn't whites be called caucasian american, asian american, latino american because i don't think its fair that other races should just be called american while blacks always has to be called AFRICAN before they can be called american while the majority of blacks have mostly white ancestors anyway just ask my friend. i know im white and all but why cant they be called american like us?