The Three Musketeers

If the novel is mostly about the adventures and development of d’Artagnan, why is it titled The Three Musketeers?

The cardinal acts almost always to protect France: Queen Anne’s affair with the Duke of Buckingham threatens war and invasion, while the continued existence of La Rochelle is a danger from French Protestants and from England. Why does Dumas characterize the cardinal as nefarious?

Compare two or three secondary characters, such as Treville, Bonacieux, or Lord de Winter. Explain their significance in the novel. How does Dumas use them to touch on larger issues?