We cannot write your essay for you but we can help you locate the poetic devices.
This is a great anti-slavery poem by Longfellow. In it, he describes an African king who is lying in a field of rice, bound for life as a slave.
There are many metaphors in the poem. Here is an example of a metaphor (sleep is compared to mist and shadow):
Again, in the mist and shadow of sleep,
He saw his Native Land.
Wide through the landscape of his dreams
The lordly Niger flowed;
His dreams are compared to a landscape.
Here is a simile:
Before him, like a blood-red flag,
The bright flamingoes flew;
He compares the flamingoes to a flag.
There are two examples of personificatiobn in the following:
The forests, with their myriad tongues,
Shouted of liberty;
And the Blast of the Desert cried aloud,
With a voice so wild and free,
The forest having a tongue, and the desert crying aloud.
Write about how the poetic devices make a strong anti-slavery statement.
There is information here on enotes about Longfellow.