Every time I meet or hear/read about someone named Marcus, it’s almost always a black guy. I have known one white Marcus in my life; his father was German. I gather that Marcus is a German name. It seems to be exceptionally rare among white people in America.
Why Marcus?
It’s Roman, maybe from Etruscan. But yeah most white Marcuses I’ve heard of were German.
I suppose respect for Marcus Garvey had something to do with it.
Garvey seems a reasonable hypothesis for the start (although where did his folks come up with the name? 
)
At some point, it probably just became a common name in the community - just like you see a lot of white John’s.
Marcus is a Roman name, from the god Mars.
Roman names had a long popularity in black communities after slavery. Cassius Clay was a junior, for example, and his father was named after a white abolitionist. Rome was a symbol of republicanism in the early America so lots of Roman names existed in the white community before the Civil War. When blacks started being able to name themselves, it seems likely that they chose names popular or meaningful for the period.
As an aside, I personally love the fact that Black/African-American women name their children such unique names. The world is boring when all you have are Johns, Davids, and Michaels.
Seriously.
I wish my mother had named me something unique.
I know this is what all the baby name books say, but it is not correct. Mars, gen. Martis, looks nothing at all like Marcus, gen. Marci, other than the same first syllable. True, -c- and -t- get confused in Medieval Latin, but not in Classical Latin. Plus Old Latin is Mamors, even less like Marcus. As far as I am aware, the actual etymology of Marcus is not known.
And just to add, I know a couple of white Marcuses, one of whom is under 10 and the others of whom are in their 40s.
Marcus Allen was a very popular black running back in the 80’ and part of the 90’s.
Kids are often named after sports figures.
Also a lot of African American males do not like to shorten their names. I know a lot of African Americans named James, not Jim; named Terrence, not Terry; Andrew, not Andy and so on.
Mark, Marc, Marcus, don’t seem to be that common names. I have only known one or two named that or their variants. So when you hear Marcus, it may seem more common among African Americans as others may shorten it to Marc.
Yes, Marcus is common, but I don’t know if there is a solid reason. Why is Aiden so trendy now among white folk? Because people here the name and like it. I don’t think it’s anything more complicated than that.
I grew up knowing several Marcuses and a Demarco.
“Gagundathar” is not unique to you?!
I don’t know enough to comment, but I took the information not from a baby name site but etymonline.com. They’re usually pretty solid.
The actual derivation, fortunately, is irrelevant to the Roman connection, which is real.
Interesting that you say “women” instead of “parents”.
They’re only as good as their sources, and given names are notoriously difficult with regard to etymologies. The Marcus < Mars works as long as you don’t look too closely. There’s a plethora of data, including the name Mamercus, which does seem to be from the god. As you say, irrelevant to the discussion here, anyway.
My college roomate was named Marcus, and he was white. He was from Texas.
Just seconding (or thirding) this. I’m sure Marcus Garvey was the seminal inspiration.
Maybe it’s more that most of the white guys named Marcus go by Marc or Mark instead. I only know one white Marcus who goes by his full name, but several Marks or Marcs.
Also pointing out there are lots of Marks & Marcs who are not using a short form of Marcus. Their given names really are Mark or, less commonly in English-speaking countries, Marc.
I’m not black…
Gagundathar, would you enjoy having to spell and/or pronounce your name every time you met someone new? My mom hates it-