What criticism of American society did Henry Wadsworth Longfellow have?

Longfellow's famous poem The Slave's Dream was the strongest criticism on slavery then prevalent in America. By bringing to forelight the plight of a captured African negro who was a King there and his remembrances of his beloved native land and dear family, H.W.Longfellow moved the American minds against the tyranny that was slavery, brought to American soil by Great Britain. This poem was one of the greatest and earliest criticisms on the evils of the then American society.