The sea
The sea is a symbol for changing seasons, because just as a storm could shipwreck a voyage, time itself brings changes to life. For instance, the poet mentions Portuguese ships coming from the ocean to radically disturb the continent of Africa through colonialism. The sea is a mythic symbol for chaos, typically, and this is no exception. Water is a sign of life through time, just like the tide and weather cycles.
European colonialism
The Kenyans are furious at Europeans. In America, those violent Kenyans who resist are viewed as terrorists, and the poet understands that point of view, but he also knows that the Kenyans are disenfranchised against the business ventures of powerful European entities who have historically exploited Africans. The motif is complete when "The Sea is History" describes the imagery of Europeans coming to land.
The Biblical allusion
This poetry explicit alludes to the Bible. The story of the Bible is likened to the grand narrative structure of the story of life. Just as the stories in the Bible are scandalous and controversial, so is the history of the earth, especially the scandalous relationship between Europe and Africa. The allusion is pertinent because the poet finds himself in America where the Bible is frequently cited. He ends up questioning the merit of the book, suggesting that perhaps the winners are writing a one-sided history in the Bible.
Metal versus nature
One motif that comes up is how America looks to his eyes. Compared to the nature of Africa, American cities are almost rejections of nature, because there are wide swaths of metal and industrial surfaces. American power is symbolized in this, but America's problems are also signified, because one might say that nature played an important role in life, and Americans forgot it by leaving nature to live in big metropolitan areas.
Death and severity
In terms of the poet's intent, it seems that to the poet, these observations are life and death. They are of the utmost importance. Just like light and dark, the poet sees that life implies its own opposite. The reason that death comes up is probably because of the death that was occurring in Africa because of systemic issues that led to violence. Then, in America, everyone seems so perfectly happy and distracted, because the poet is thinking about death.
