(2) Sea Level
Sure, you have to know a little bit about the history of the world to figure out that Angelou is re-creating a broad-strokes version of African history here. But even if you missed every single day of social studies class ever, you'd still get the general picture. Africa's had a history of suffering. But it's also had a longer, older history, one that pre-dates the slave trade – which is what Stanza 1 makes clear to us.
Frankly, this poem is about as easy to digest as any poem with four-syllable lines could be. We're not saying that the poem's a walk in the park. We're just saying that Angelou keeps it simple so that we won't miss her point.