In the poem, “The sea is history” by Derek Walcott as the title says is about how the ocean carries a rich history. Specifically of the slave trade, of those who were carried over the sea to a new land by force. Of those who did not make it. From the very first few lines, Walcott empathizes the identity of those people. Those who suffered making it across and from those who couldn’t.

Where are your monuments, your battles, martyrs?
Where is your tribal memory? Sirs,
in that grey vault. The sea. The sea
has locked them up. The sea is History.

This first passages in a way speaks more on their culture and identity than any historical account could. Setting the tone of the poem that this isn’t simply a tragedy because slavery was awful. Or even why it happened. It laments the true tragedy that the culture, identity, and memory of those who suffered during the slave trade have been ignored in historical accounts. In the way people learning/reading about them only see it was tragic. Not of who they were. As written in these lines below.

and that was Lamentations—
that was just Lamentations,
it was not History

What these lines mean is the historical accounts are focused not on the slaves themselves. Which is why in the poem’s beginning lines Walcott wrote how the sea recorded their true history. Keeping it in locked for those who wish to dig deeper.