Unfortunately, this is one of those questions where the premise has to be questioned. I’m not sure we can say there were no “empires” in pre-Columbian North America.

First off, it’s important to debunk the widespread misconception that there was no settled urban civilization in North America, just small villages and nomadic tribes. In reality, remains of sizable towns and cities have been found dating back thousands of years. One of the oldest complex sites is Poverty Point, built 1700-1100 BC, though archaeologist argue over whether it was a permanent settlement or a periodic meeting place. The largest known settlement in North America was Cahokia, a city in what is today Illinois, which flourished in the 11-12th centuries AD and had a population in the tens of thousands (small by today’s standards, but larger than many urban sites in Europe at the time).

Cahokia is the largest known site of the “Mississippian” culture, a civilization which was settled along the rivers of the eastern United States from the 9th-16th centuries AD. The Mississippians are most well known for their large earthwork mounds, which were constructed in many of their urban sites. They were also sophisticated artisans and copper workers. Take a look at this copper plate. Looks Mayan? Nope, Mississippian, found at the Etowah site in Georgia. Of course, all of this doesn’t necessarily mean they were an “empire”.

Next, we have to define what an “empire” is, as it’s a term with different definitions depending on the context. If we are using the Aztec and Inca “Empires” as our frame of reference, then I think it’s best to use the basic, Merriam-Webster definition:

a major political unit having a territory of great extent or a number of territories or peoples under a single sovereign authority

This definition is broad enough to include most civilizations you probably think of when you hear the word “empire”. Unfortunately, it’s also broad enough that there can be significant debate over “edge cases”.

For instance, take the confederations you mention. These were major political units, which covered vast territories and included many different peoples. But were they “sovereign”? That’s a trickier issue. The probably most famous example, the Haudenosaunee (Iroquois) Confederacy, was quite expansionist and pushed its control across the Great Lakes. However, it also afforded its constituent members a vast degree of autonomy, to the point where it can’t be said to have a central administration. The Powhatan Confederacy was more centralized, with a single head chieftain, but its individual tribes still held vast authority, even in matters of external relations. Personally, I would not consider most Confederations to be empires, but this is not my area of expertise and I invite other authors to give their input.

The far more pertinent issue, however, is the lack of written record. We have very little in the way of any written record for pre-Colombian civilizations. The Maya script is the only system of writing that has been substantially deciphered (and it’s possibly the only complete pre-Columbian system of writing to exist at all), and the pre-contact Maya still have large parts of their history and society that are unknown or uncertain.

Because of this, it’s hard to say what political organization anywhere in the Americas looked like centuries before contact. We know of the Aztec and Inca “Empires” because they were around when the Spanish arrived. I think it’s plausible that, if these empires had fallen pre-contact, we wouldn’t conclusively identify their various sites as belonging to a united polity.

However, it’s particularly hard to say whether there were any “imperial” systems among the Mississippian. The Mississippians suffered what could be termed a “civilizational collapse” between the 15 and 17th centuries. The exact causes aren’t known and are still debated, but one theory is that the beginning of the global cooling period known as the “Little Ice Age”, with the period of 1400-1500 being particularly chilly, reduced crop yields, resulting in increased conflict and fragmentation. When the earliest European explorers arrived (early 16th century), they may have caused a series of epidemics, devastating what was left of the Mississippians at that time.

In any case, by the time significant numbers of European settlers arrived in their homelands (in the 17th century), the Mississippian civilization had long collapsed, nearly all their urban sites were abandoned, and their descendants were organized into the smaller villages, tribes, and confederacies most people today are familiar with. To these nations, the great mound cities were already a distant memory. Thus, there was little of Mississippian history that could’ve been recorded, even if European settlers had bothered to try.

It’s very possible that among the Mississippians, there may have been powerful polities one might term “empires”. It’s possible that there may have been many “empires” in pre-Colombian history. Unfortunately, we don’t know, and we probably never will.