What were the effects of the transatlantic slave trade?

The effects of the slave trade were numerous and enduring. They are, arguably, still being felt in our present day. 
The two most important effects to consider are economic and cultural.
The New World, particularly the United States, built its wealth off of slave labor. Around forty-five percent of Africans who were captured on the western coast of the continent were shipped to Brazil. Another forty-five percent went to the British, French, and Spanish colonies in the Caribbean. Only around five percent were sent to the thirteen colonies that would become the United States. The number of slaves would significantly increase during the eighteenth and nineteenth centuries due to the practice of "breeding" slaves, to not even mention the impact of rape and concubinage. The remaining five percent of slaves were scattered around Mexico, Central America, and other parts of South America. 
Industrialists and planters reaped vast amounts of wealth off of cash crops, such as sugar, rice, and cotton, due to the ability to obtain free labor. Furthermore, slave labor could be exhausted in ways that would not be tolerated by whites working in indentured servitude. The ability to force someone to work in extreme weather conditions or for exceptionally long hours, out of fear of torture or death, extracted more labor from the individual and, thus, more capital. This capital not only brought wealth to the white planter class in the New World, it also contributed to the wealth of the European nations which held these territories. They used the cash crops to fuel their industries, such as the use of cotton for textile plants. 
Another major effect of the Atlantic slave trade was cultural. Certain instruments, such as the drum, were introduced to the New World. Despite the objection of many slave owners, slaves continued to play the drum in secret and eventually, it became a legitimate and widely accepted musical instrument. The cultural impacts of slavery are myriad, but it had a profound impact on music, particularly the development of spirituals, which led to blues and jazz. These are uniquely American forms that would not have occurred without the descendants of slaves. In South America and the Caribbean, samba and salsa developed from the same influence.