There is a fairly strong divide between the african-slaving Americas and the native-slaving Americas, at times even within colonial territories of the same empire: Spanish Argentina overwhelmingly used black slaves, while Peru and Mexico, also Spanish colonies, dominantly used natives as slaves. Of course, these are trends, and there are always exceptions/examples to the contrary: native slaves in regions where African slaves were the norm, and vice versa.

However, these trends did exist. And they were linked, most dominantly, to the lifestyle of the natives in a given colonial region. Such is the divide between slavery in Mexico versus the United States. During the Spanish conquests and the establishment of the first colonies in the Americas, the Spanish were met with distinct societies: kingdoms and tributary states with long term settlements, agriculture, and generally a society that, while distinct to a degree which European scholars of the time couldn't even convey appropriately, was fundamentally more similar to the feudal European way of life than, as I'll explain later, the lifestyle of the north American natives.

As such, this similarity to Europe yielded a populace which was relatively populous and had a tradition of agriculture and sedentary life. As such, Spanish conquistadors, when given land as a reward for their services to the crown in a phenomenon known as Encomienda, their estates in the new world were "staffed" with natives, forced to work for the lord and just as vulnerable to his whims as plantation slaves in the US would be to their master's. Exploitation and mistreatment were similar in both fashion and frequency to US slavery. The largest distinction in this event would have to be that the Spanish justified their slavery in a much different way from Americans, and slaving never became as integral to social order as it did in the American south.

Now, onto what I think was your intended question: why did English and French colonists, especially in North America, as well as the post-independence United States prefer African slaves over enslaving native tribes? Well, the answer to this lies in the inhuman utilitarianism of maintaining a slave economy. What is an ideal slave population? One that is in abundant supply, hopefully is culturally acquainted with agriculture, and is easily accessible to the individual seeking to establish a plantation. Colonial economies relied to an extreme degree on plantations: a new product that grew best on colonial land, which was in short supply in Europe but abundant in the New World always brought a great deal of profit. But to establish such a plantation, one needed slaves, and not just a few. North American natives, the various tribes across what would become the United States, were not ideal for commercial slavery. They lived mainly nomadic lives, often still reliant primarily on hunting and non-sedentary agriculture, with no real long term settlements like towns and cities. Their populations, while substantial, would not have fulfilled even a fraction of the demand there was for slaves in the newly forming colonial economy. Thus, importing and justifying the enslavement of Africans was easier and more immediately profitable than (and I truly hate to use these words when talking about humans) gathering and breeding native slave populations which could satisfy the demands of the plantation economy which dominated colonial regions following their establishment.

The short answer to this is that indigenous people in the Americas were enslaved -- there is plenty in our FAQ about this. For more on African slavery and the slave trade, hit this link.