It is interrogative because a question is being asked. It is usually interrogative if there is a question mark at the end.
Answer:
They don't have many similarities other than both being functional sentences.
However, you can make a compound sentence with a run on.
Answer:
Du Bois certainly is an important thinker, but a poet? Yes, a poet. The paraphrase 'late land of slavery' is from a poem.
