The first sentence of your post could be seen as an example of the government's strategy of pitting "Blacks against Mexicans for scraps."
I'm not saying that's how you meant it necessarily.
Look at a couple of things. First, what is this "urban America"? Don't adopt babylon's double talk and euphemisms brudda. I know they can absorb into you by a process of osmosis from constant bombardment with them, but we should consciously be trying to avoid saying things like "urban america" or "collateral damage". Say "U.S.-born Black African people in the U.S." if that's what you mean, just like the reporter should say "mangled dead bodies of innocent civilians" when that's what s/he is supposed to be describing.
Now, the Blacks vs. Mexicans part.
Do you mean "U.S.-born Blacks vs. immigrant so-called Latinos"? or "vs. immigrants" in general? I'm sure you are aware that a large number of immigrants, "illegal" and otherwise, in North America come from places such as Haiti, Jamaica, Guyana, etc., not to mention various areas of Africa, and could certainly be described as dark skin kinky hair Black Africans.
Some "Mexicans" are also Black Africans. And "Mexicans" are not synonymous with "Latinos". In Oregon where I used to live and where I worked with an organization fighting for immigrant rights (amongst other things), there were certainly as many Guatamaltecos, Salvadorenos, etc. etc. as Mexicans. Many if not most of these people are puro indio, Mayan etc. i.e. the indigenous people of the Americas.
On the east coast you would find more people from Spanish and French speaking caribbean countries, many of whom are Black African or have significant percentages of Black African blood.
Now as far as the marches, I don't see them as no part of no ploy to pit Blacks against Latinos (bearing in mind that "Blacks" and "Latinos" are not mutually exclusive categories), nor as an example of how "newcomers" have been able to make great gains while generations of African descendants in the U.S. continue to be held back (not saying that this remark does not have some truth in it... but these sort of examples, I have noticed, are often trotted out when someone wants to make an over-simplified point about "look how much better organized those Latinos/Jews/Asians/whoever are than us, we need to be like them". Not saying that's what you're saying.)
I see the marches as a result of mobilization and organization within the communities that would be most affected by the neo-nazi criminalization-of-immigration legislation. Communities which include people of Indigenous North, South and Central American descent, African descent, Asian descent, various combinations of the above, etc.
Black African people WITHOUT A DOUBT played a significant role in organizing and participating in these marches. 2 million people marched in over 100 cities just now. Who do you think was marching in Florida, white Cubans?
These marches are also part of a tradition of resistance which was largely created and maintained by Black African people in the U.S.
Bear in mind that when the American Indian Movement, Young Lords, Brown Berets, etc. started organizing in the ghettoes, barrios and reservations of the U.S. in the 60s and 70s, they were inspired by the example of the Black Panther Party for Self Defense.
It takes much more than marches and changing a couple pieces of legislation to create real change for the better for poor people of color in the U.S. and worldwide, but these marchers are stepping in the right direction.
As for the MMM etc., well of course they will always try to downplay the amount of people at these things. (When they admit that 2 million people marched just now, you know that it was really 3 or 4 million).
Now none of this is to say that there is not varying degrees of conflict in various areas between immigrants of various races, and U.S.-born Black people. Certainly the system deliberately exacerbates such conflicts, both directly and indirectly through its saturation of messages throughout the world... so that some Latinos (including dark-skinned Latinos with African blood) may come to the U.S. ready to look down on African "Americans" as inferior; and so that some African "Americans" look down on Haitians as inferior.
Anyway I gotta go to work. (I wonder if any unemployed Welsh people are mad that I'm "taking their job"? Well eff em, I'm Welsh too anyway.) Mainly I just wanted to say that African so-called "Americans" should never get into the position of even implicitly supporting the crackers' borders across the North American continent, or anywhere in the world. U.S. Out of North America. Peace Out.