What does this stanza mean

They tell me thou art rash and vain,

A searcher after fame;

That thou art striving but to gain

A long-enduring name;

That thou hast nerved the Afric's hand

And steeled the Afric's heart,

To shake aloft his vengeful brand,

And rend his chain apart.

Sounds like someone is being told about someone else, and they're being told this person is selfish and vain, and that they are putting in a lot of work into some kind of selfish gain. This a well-known person (long enduring name). This person did something wrong to Africa/African people. I'm not entirely sure in the last two lines.