While Native Americans did (and still do) suffer from the genocidal colonization of our lands and lost much of our population as a whole, I do not agree that we were "practically pushed out of existence."

According to the 2010 United States Census report, those who solely identify as Native American and/or a combination of Native and other origins number between 2.9 million and 5.2 million. This is between 0.9% and 1.7% of the total population of the U.S. in 2010. Granted, this isn't a large number in comparison to other racial/ethnic groups. But it isn't a small number and it grows every year.

Much evidence suggests that Native American populations did suffer greatly due to diseases. However, the numbers are hard to pin down and we cannot say if it was greater than or less than 95% of the total population (a common number people like to throw around for this topic). And of course, the acts of genocide decreased number further.

A big reason we see the Native American tribes being much more adversely affected is due to geography. Much of Africa is desert, Savannah, and jungle. Much of it was a harsh environment. At the time, much of inland Africa that contained valuable resources was landlocked and didn't make it as economically viable as the Americas at the time - which heavily bordered the oceans and had vast river networks - since a primary way of shipping was with a sea-route. And in general, the Americas were more hospitable to expansion and settlement at the time. See this thread for sources.

With the weakened population density from diseases, financially profitable resources drawing in more foreign powers/colonizers, and favorable geography that made it relatively easy to spread across the land (in which most of the land was rich with resources), it is no wonder that colonists covered the Americas rapidly and eventually outnumbered the remaining native populations. With the following racism, colonization, and genocides, native peoples in the Americas underwent even more brutal treatment until basically the whole continent was taken and many were killed off.

And while many natives are still experiencing the consequences of this, we are still here. We were not wiped out. And we will continue to grow. Check out /r/IndianCountry if you're interested in learning about Native American affairs, news, and culture.

Also, I think it is important to point you to the FAQ concerning Africa. You might be able to get a better answer there and it also shows that much of Africa was, indeed, affected in population and culture by colonization.