By the time there was a United States of America, the use of African slaves was pretty set in stone, but as the Americas were being colonized there were other options attempted. Notably natives, though that didn't really work because the intense labor killed many(along with disease) and since they already knew the land, many would just up and leave and there was no way to track them down considering they were adept at surviving outside of the territory the Europeans had colonized. Europeans would also basically sell themselves into slavery for the chance to start over on the new continent. It was more accurately an indentured servitude, but it was uncommon(especially early on in the colonies history) that they would live to reap the benefits of there service. In the end, Africans just made the most sense since they were cheap, already exposed and immune to many European diseases and easy to acquire. You would not see slaves from Egypt(which is an African country btw) simply because it was easier to get them from the northwest coast of africa instead of the far east corner of the Mediterranean and similarly it would not be sensible to get workers from China as you would have to sail them all the way around the world to reach the colonies in the Americas. Pirates wouldn't generally bring in slaves, but I suppose it is possible they would drop an Egyptian slave off, I've just never heard of such a case.

I hope this answers everything. I wrote it out on my phone which I am not so good at.