In Henry Wadsworth Longfellow's poem, "The Slave's Dream," the layered meaning of the poem can be found in the literal interpretation that we are reading of the dream of a slave who was once a king in his homeland, or it can be seen as the capture of any man (against his will) in his native Africa.
The poem begins by describing a slave, lying in the field where he has been gathering rice. This is not the first time the man has had this dream of home, as we note the use of the word "again."
Again, in the mist and shadow of sleep
He saw his Native Land.
As the landscape is described, what comes quickly into focus is the man's wife and family. One might assume that this slave is a king (as the speaker notes) in Africa, or that any man with wife, children, home, and freedom, is a king.
He saw once more his dark-eyed queen
Among her children stand;
They clasped his neck, they kissed his cheeks,
They held him by the hand!
As the man rides along the banks of the Niger River, the image of "chains" with "a martial clank" may be literally as they are described, or they might refer to his captivity by slavers on the beach. Then before the "king," there is "a blood-red flag" of flying flamingoes, but perhaps there literally is blood as other would-be captives are whipped or killed in the attempted abduction. As the "ocean rose to view," perhaps the man has his first glimpse of a slave ship on the water.
As a captive...
At night he heard the lion roar,
And the hyena scream…
These animals may represent nature's horror to see something so unnatural taking place...as it might seeing any creature—meant to be free—taken into captivity. The "glorious roll of drums" could be sounds from the jungle, but may also refer to drums that might have been used to "coax" the captives to march in-time toward the ship that would carry them to death or to lifelong servitude. Perhaps the forests seem to be speaking; on the other hand, maybe the sounds represent the variety of languages of the captives, the different dialects, as these people beg for freedom:
The forests, with their myriad tongues,
Shouted of liberty...
The speaker notes that this man, once a king of his world in some manner, has been carried in death to a "Land of Sleep." He does not feel the slaver's whip; he does not notice the burning sun overhead. His body is nothing more than "A worn-out fetter, that the soul / Had broken and thrown away," for the slave no longer has need of it and has ultimately triumphed over his enslavement.