The "American" slave trade is but one part of a larger "Atlantic" slave trade- that saw slaves taken even beyond the Americas or island-Atlantic. Only a fraction of slaves were taken to continental North America.

So at the very least we can say, no, the American slave trade was not unique in its racial or ethnic prejudices.

However; war is most certainly an important factor in the slave trade (though perhaps not 'the' driving factor). The slaves were often the losers of conflicts within Africa or the victims of war time slave raids. What better way to get rid of your enemies than to sell them to traders who intended to carry them across the sea? Of course, the economic profit from this trade also plays a role in increasing warfare and increasingly centralized and belligerent states along the coast of Western Africa.

Like others; I am exceedingly curious why a course on Ancient China spent so long on the American Civil War?

The Bible has verses condoning ethnicity-based slavery which suggests the idea is much older than the American slave trade. The specific passage is Leviticus 25:44-46 -

As for your male and female slaves whom you may have—you may acquire male and female slaves from the pagan nations that are around you. Then, too, it is out of the sons of the sojourners who live as aliens among you that you may gain acquisition, and out of their families who are with you, whom they will have produced in your land; they also may become your possession. You may even bequeath them to your sons after you, to receive as a possession; you can use them as permanent slaves. But in respect to your countrymen, the sons of Israel, you shall not rule with severity over one another.

I'm not sure as to the actual details of the ancient Levantine slave trade, but the medieaval Arab slave trade banned the enslavement of Muslims which lead to Christians and sub-Saharan Africans being imported in vast numbers, and the Africans were viewed with similar prejudices as they were in America- low intelligence, brute strength, rapists- despite the Hadith's advising against racial discrimination.

It is said that when the black slave is sated, he fornicates, when he is hungry, he steals.

Al-Abshibi

We know that the Zanj (blacks) are the least intelligent and the least discerning of mankind, and the least capable of understanding the consequences of their actions.

Al-Jahiz

Both these examples are imperfect though, as rather than designating a race to be used as slaves they designate a "race" (rather more like a religious distinction but the line isn't clear) that was protected from being slaves.

The American slave trade was multifaceted, and the demographics of those enslaved changed remarkably throughout the history of the colonies and the subsequent founding of a new nation. The Indian slave trade was not solely based on ethnicity, the English were perfectly happy to ally with whatever Native American nation provided them with captives, and the traders were likewise just as happy to instigate hostilities when that nation outlived it's usefulness in providing slave labor. In many ways the English colonial enterprises in the south, mostly Virginia and to a greater extent the Carolinas, were initially built on the trade of deerskins and Native American slaves.

Slaving, and slaving raids, became a tool of war for English once they began to establish permanent settlements in the New World. The peace established between Plymouth and the Wampanoag lasted a generation. Massasoit’s son, Metacomet/Phillip, succeeded his father as sachem and due to a variety of factors organized the hostilities now known as King Phillip’s War. When the dust settled more than 3,000 Native Americans were killed and hundreds of survivors who were not professing Christians were sold into slavery in Bermuda.

The Carolinas used slaving raids against Spanish Florida, with the added bonus that captive slaves presented another means of raising capital. Traders employed Native American allies, like the Savannah, to raid their neighbors for sale, and groups like the Kussoe who refused to raid were ruthlessly attacked. When the Westo, previously English allies who raided extensively for slaves, outlived their usefulness they were likewise enslaved. As English influence grew the choice of slave raid or be slaved extended raiding parties west across the Appalachians, and onto the Spanish mission doorsteps. Slavery became a tool of war, and the English attempts to rout the Spanish from Florida included enslaving their allied mission populations. Slaving raids nearly depopulated the Florida peninsula as refugees fled south in hopes of finding safe haven on ships bound for Spanish-controlled Cuba (a good slave raiding map). Gallay, in Indian Slave Trade: The Rise of the English Empire in the American South, 1670-1717, writes the drive to control Indian labor extended to every nook and cranny of the South, from Arkansas to the Carolinas and south to the Florida Keys in the period 1670-1715. More Indians were exported through Charles Town than Africans were imported during this period. After the Yamasee War (1715-1717) the demographics of the slave population in the south began to change, with African slaves representing a larger percentage of the total slave population and the relative number of Native American slaves slowly declining.

One final note, ideas of race and ethnicity are nebulous, their perceived boundaries and definitions change dramatically over time and between cultures. We run into serious issues when we apply our modern perspective of the terms to the past. We should be particularly wary of applying blanket statements about the role of ethnicity on the sale of humans over the course of multiple centuries.

So, your question is a really interesting one, and needs to be dealt with in parts. Let's knock out a basic answer first though. Was the slave trade and the institution of slavery in America unique, in that it was implemented on the basis of ethnicity rather than for economic reasons or as a result of conflict? The short answer to this version of your question with a narrowed scope (to what I think you might have meant) is no.

Here's a longer answer:

So if we're talking about slavery, we have to distinguish between the various types of slavery. You've already started doing this by asking about the reason for enslavement, but I'd like to deal with it in two groups: chattel slavery and non-chattel slavery. Chattel slavery means that one person is quite literally the property of another person. When a person is reduced to property, rather than considered a temporarily or permanently enslaved person, well then you get a lot more of the excesses and atrocities that you've no doubt heard about in association with slavery. That isn't to say that this isn't true for non-chattel slavery though. For example, the forced labor imposed by the Portuguese upon the Brazilian natives at potosi or the conditions imposed by king Leopold in what is now sometimes referred to as the Congolese genocide certainly would be considered just as unconscionable as anything associated with chattel slavery in the U.S..

But, let's deal with non-chattel slavery first. If we're talking about non-chattel slavery, then we're basically talking about forced labor - an institution which is much older in its widespread form than widespread chattel slavery. Here, we might include everything from the Old Testament practice of temporary enslavement to the practices of colonialism in the 17th, 18th, 19th, and early 20th centuries. I've already mentioned the Portuguese and silver mining, as well as King Leopold and the Congo (you really should try and read the book King Leopold's Ghost if you're interested in colonialism or forced labor). The British use of what they called 'transportation' as a punishment was quite common, wherein criminals would be exiled to a particular colony for a period of time, and in some cases auctioned off as indentured laborers for the duration of their sentence (A Commonwealth of Thieves, by Keanally, has a great introduction to this in the first chapter or so). So while forced labor wasn't necessarily always implemented because of ethnicity, there are numerous examples (like that of the Portuguese or that of the Congolese genocide) where it was implemented based primarily on ethnicity. I included the Congolese and Hebrew examples just in case you meant slavery in the Americas, and not just in America (meaning the good old U.S. of A..

Now, as to chattel slavery, the Portuguese were known to practice chattel slavery (using people from Africa) in their various and sundry territories, so it was used outside of America and outside of the Americas too. (Though I'm no expert on the matter - I only ever cared to study the Portuguese colonies in the Americas and in Africa.) The British brought slaves home to their island, and most of their imperial domains as well (the empire wide abolition of slavery took effect in 1834). So if you meant chattel slavery outside of the Americas then these examples pretty much cover that. (Freedom burning by Huzzey (sp?) covers abolition in the empire very very briefly).

I can't speak to chattel slavery outside of the Atlantic trade outside of the same time period as slavery in the Americas, so someone else will have to tackle that one. But, there's your slightly longer answer. Sorry for the formatting and shoddy cites, I'm writing this on my phone.

Many African groups traded prisoners of war to the Europeans for guns. This certainly perpetuated war in Africa. Most African slaves went straight to Brazil, where they worked plantations. This was a huge money maker, so economy certainly played a role.

EDIT: tribes -> groups

I know the idea of ethnically based slavery dates back to ancient Germany and Scandinavia, as supposedly (kinda like the castes system in India) the social classes all descended from three kids Heimdall had whit three different women, each of them became the slaves, the craftsmen and farmers, and the rulers and hunters/warriors respectively. Of course, this wasn't the reason they had slaves, but it was the justification, just as ethnicity was the justification used in the late Atlantic slave trade, so probably the idea of race-based slavery is as old as races themselves.

To clarify your question, when you say "economy," are you referring to the economic need for slaves in general, or that say, white poor people weren't considered eligible for slavery, while black poor people were?

I know the idea of ethnically based slavery dates back to ancient Germany and Scandinavia, as supposedly (kinda like the castes system in India) the social classes all descended from three kids Heimdall had whit three different women, each of them became the slaves, the craftsmen and farmers, and the rulers and hunters/warriors respectively. Of course, this wasn't the reason they had slaves, but it was the justification, just as ethnicity was the justification used in the late Atlantic slave trade, so probably the idea of race-based slavery is as old as races themselves.

What about the Hungarian feudal system enslaving Slovak?