There is no credible evidence that African Americans, or any Africans, contain a larger component of genetic material from the original nation of Israel, whether of the southern Jewish kingdom or the northern kingdom that was dispersed earlier. However, African Americans, and every other group of people, have the opportunity to be adopted by faith as children of Abraham.
Galatians 3:28-29 There is neither Jew nor Greek, there is neither slave nor free, there is no male and female, for you are all one in Christ Jesus. (29) And if you are Christ’s, then you are Abraham’s offspring, heirs according to promise.
Colossians 3:11 Here there is not Greek and Jew, circumcised and uncircumcised, barbarian, Scythian, slave, free; but Christ is all, and in all.
Acceptance as spiritual children of Abraham applies equally to all nations. I am not American, but Australian. My ancestors mainly came from the “barbarians” of the British Isles, including one who was a convicted criminal transported to Australia, not merely an innocent kidnapped person as were many of the ancestors of the African Americans. Exactly the same conditions apply to me as to every other person from every other group. Faith in Christ allows anyone to be accepted as spiritual descendants of Israel and therefore heir of the promises.
Additionally, the person who asked the question in the title of this answer also said:
If [African Americans are] not [the dispersed remnant of Israel], then why does it seem like we’re cursed? It’s been nothing but hell for me all my life and I’m sick of not being favored, even by God.
I am sorry to hear that you feel that your identification as an African American means that you suffer. I assume that you mean that you suffer discrimination and less opportunities. There have been many cases throughout history of groups who were unfairly discriminated against. For example, the people of Israel in Egypt who were persecuted and eventually rescued by God in the days of Moses. Israel was also told that they would be exiled from their land and suffer persecution in the lands of their exile. I can understand why you might see a parallel between exiled and persecuted Israelites and your ancestors. However, just because a group suffers discrimination does not mean that they are themselves descendants of Israel. When expressed logically it can be seen that this does not follow: “Israel was persecuted; African Americans are persecuted; therefore African Americans are Israelites.” This would be like saying: “Cats have fur; this animal (a rabbit, actually) has fur; therefore it is a cat”.
We know from his involvement with the Israelites, though, that God is a God who does care for people who are suffering (cf. Ex. 3:7-8; 1 Sam. 2:4-8). Relief might not come until Jesus returns to the earth, but one day it will (Acts 14:22). Having this hope calls a Christian to persevere through suffering (Rev. 2:8-11).