Well, depends on your unspoken terms, really.

Haiti was a country that did and does exist, if you want to talk about the U.S. in particular Liberia is a country that did and does exist. If you want to keep things to the American mainland, the Seminole - who came from fugitive slaves as much as North American autochthons - had effective sovereignty over the Florida peninsula for a while, there were other maroon colonies besides.

If you’re talking about the ‘60s wave, Amerikkka was never going to let a definitionally oppositional state establish from its sovereign territory in the middle of the Cold War, come the fuck on. (That same Cold War pressure also brought things like elite accomodation to black demands and the replacement of the draft with an all-volunteer military so as to keep eyes on the prize and not internal race war.)

I think a lot of contemporaries realized that and so the more practical enthusiasm got channelled into pan-Africanism as decolonization proceeded apace. There were GOING to be Westphalian states run by blacks for blacks, with borders and institutions, and hopes were high.

T’Challa, Marvel Comics’ “Black Panther” that’s getting some heat right now, is a daydream of those diaspora hopes for post-colonial leadership - a strong, noble philosopher-warrior-leader who drives his particular country on to technological self-sufficiency, then dominance (South Africa managed to build a modern economy, jet-set cities, and a nuclear military on a base of black labor, after all) while standing up for all of Africa as a continent and a people.

(You will remember that Rastafari, originating in the early 20th century in the black diaspora, holds early pan-Africanist Marcus Garvey as a prophet and Emperor of Ethiopia Haile Selassie - at establishment head of the only indigenous government in Africa - as a messiah.)

In practice, the warrior leaders weren’t that noble, the philosophers weren’t that strong. Rather than standing for Africa entire, the newly independent countries engaged in border warring (that was largely Cold War shit - after the Sino-Soviet split a lot of countries got to host 3-way proxy wars, which no doubt was fun). Rather than even standing for their own countries entire, politics tended to shake out along lines of tribal identities that were meaningless in the diaspora, with at best an ideological gloss that was efficiently shed with the collapse of the Soviet Union.

All that said, I think an alternate history (or future) where this panned out, and maybe drew return migration from the diaspora is still more likely than the establishment of a black-identity state on North American mainland.

I think rather than an encompassing concept of “blackness” organically emerging from the wisdom of the native African people, this would likely involve a founder state establishing an “African” identity that’s heavily salted with their own particularity, expanding across the continent, brutally suppressing other local identities over the course of several generations in favor of this “Africanism” in a way that uncomfortably reminds of European colonialism, and that any inspirational “pull” factor on the diaspora would be matched by a “push” factor as other states increasingly consider inhabitants sympathetic with the identity of this rising power to be suspect aliens, but hey.