if no, why did they not, was it European Invaders?
As /u/RioAbajo said, an empire is usually defined as a multi-ethnic polity^1 in which one ethnicity has dominant status over the others. This can often be hard to determine archaeologically, especially in North America where we don't have, for example, mints producing standardized government-issue coins. Where we see a widespread material culture, are we looking at a single political culture, or several related ones? Where we seeing differing, but neighboring material cultures, are we looking at two independent political cultures or is one political dominant over the other? This can be exceptionally hard to parse out.
Let's use Cahokia as an example. Between 600 and 1000 CE, Cahokia was one of many similarly sized large towns along the Middle Mississippi valley between Illinois and Missouri. Around 1050 CE, there's an explosion of monumental construction, starting with the Grand Plaza and Monks Mound. The population of skyrockets, reaching a peak around 1200 of between 20-50,000. Through the 1200s, this population is increasingly siphoned off to outlying communities - first the smaller cities that surrounded Cahokia, then to their subsidiary towns.
Now, given the size of Cahokia and its immediate neighbors in the St. Louis area, they wouldn't have been able to produce enough food locally to sustain themselves. The scarcity of tools related to farming in area compared to the population further indicates that the people of Cahokia weren't doing a lot of farming themselves, despite a diet rich in maize. This all indicates that they had reliable access to crops grown elsewhere. One of those agricultural areaas appears to be the Richland Complex to the east of Cahokia, where there's an overabundance of farming equipment. The most common tool is a hoe made from Mill Creek Chert. This is stone isn't found locally here, but comes from southern Illinois, showing that the people in Richland had reliable access to the quarries in the south. Near these quarries is a small Middle Mississippian town known today as the Hale Site, which seems to have been responsible for exporting the hoe blades north to Richland and to a lesser extent Cahokia. The Hale Site is very close to a larger Middle Mississippian site known as Kincaid, which was either a tributary of Cahokia itself or separate polity too weak to keep Cahokia from dominating a lucrative resource on its doorstep. A lot of small Middle Mississippi towns affiliated with Cahokia in some fashion seem to pop up near important resources. Other examples includes the Collins site near a prominent source of salt close to the Indiana border and the Redwing and Aztalan sites in the Minnesota and Wisconsin, respectively, which seem to have been funneling copper from Lake Superior down to workshops of Cahokia. Redwing and Aztalan are particularly interesting because, while they're clearly Middle Mississippian, they're deep in Oneota territory and isolated from all the other Middle Mississippian towns to the south. Do these towns represent some sort of administrative centers from which the Cahokians could dominate the local Oneota peoples? Do they represent far-flung trading colonies? Or are they political independent Middle Mississippians who moved north to take advantage of a lucrative trade route?
Historic Mississippian polities might shed some light on the situation. For the most part, they were all multi-ethnic, with particular town dominating the others, demanding tribute, and able to mobilize force to extract that tribute when denied. The Appalachee from northern Florida were the first Mississippians to encounter Europeans. They were mostly mono-ethnic, but there were some tributary Timucua communities on their eastern border. Prior to European contact, they might have had control over more Timucua towns. Many Timucua leaders used the title "holata," which was the Appalachee term for tributary leaders beneath the nico. Cofitachequi in South Carolina seems to have been largely populated by Siouan-speaking people (later known as the Catawba), but the leadership seems to have been Muskogean-speakers. In terms of geographic size, Coosa is the largest pre-Columbian polity that we can confirm in what's now the US (others might have been larger but their full size remains unknown); it stretched from the Virgina-Tennessee-North Carolina tr-state-area down into central Alabama, with its capital - Coosa - in northwestern Georgia. It's leadership were Muskogean-speakers again, but the population of the region would have included the Yuchi and probably some Cherokee as well, and even the Muskogean-speaking population wouldn't seen itself as a single ethnicity. Along the lower Mississippi River at the time of European contact, Quigualtam was the dominant power. Its leadership appears to have been Natchezean, but among its tributaries were Tunica-speaking peoples who tried to get the Spanish to help them revolt and failed. When de Soto demanded that Quigualtam (often the leaders of Mississippian polities take the name of the polity as their title, or in a few case, its the other way around) come and tribute to Spain, Quigualtam sent back a reply saying that he was unaccostumed to making such trips and all of whom he had knowledge came to honor him and paid tribute, either willing or by force. Ultimately, the Spanish-Quigualtam confrontation would end with the Quigualtam fleet of 100-200+ war canoes (the largest class of which held 80 men) chasing the Spanish into the Gulf of Mexico.
The Aztecs were in North America, so presumably they count. There were a number of other nations in Mexico before and during the Aztec zenith. Outside Mesoamerica, writing was limited and we know comparatively less about their political structures. There were a few possibly "empire-like" groups in the Southwest including the Verde Confederacy and the Chacoans, but the nature of these polities and even their existence as cohesive entities can be controversial.