In the book, the protagonist wakes up from either suspended animation or cryo (Probably supposed to be a short test), After 10-20 years have passed.
He finds the facility abandoned (and looted?), gets to the surface and it looks like a war zone. Wreckage everywhere, smashed buildings, bullet holes everywhere. (I think he gets some gear from the facility, MREs, Water, First Aid kit, Weapons) and goes exploring to find out what happened.
He comes across a (young kid?) who is terrified of him, (maybe trapped or pinned under debris), gives him food and water and digs him out or helps him so the kid trusts him. Eventually the kid leads him to his family (mother & other siblings) who are equally terrified when they see him, but the kid convinces them the protagonist is OK, that he saved his life.
None of the children are really old enough to remember anything from before the protagonist enter the cryo test, but the mother is. He starts questioning her about what happened while he was asleep. She tells him it was NOT another country invading, it was all internal (society collapsed, food shortages, massive riots).
Later, I think they hear a large group of people approaching the (town? city? area?) where the family has been living, and the family becomes frightened again, saying the enemy is coming back.
He says he will help defend them and asks what the enemy looks like? She looks at him and say, "They look just like you." He is African American. [The implication being that African-American uprisings are what caused the riots and collapse of society.]
This might have been a short story/novella. It probably was a paperback in English published in the USA.
[I may be misremembering, maybe she did not tell him they look like you, he just went and got into a position to defend against the enemy, and when they approached, realized they were all African-American.]