The Southwest agricultural civilizations show a growth/decline cycle going back hundreds of years before contact; it's probably primarily climate-driven, although some features of the archaeological record suggest that warfare's been an issue too. European contact was just another decline, one that they managed to weather pretty well by Native American standards -- their successors are among the most intact native cultures.

The Mississippian culture didn't show that cycle, but it nonetheless was in decline for unrelated reasons at the time of contact (with Spanish explorers); smallpox and other diseases seem to have been the last proverbial nail in its coffin. Note that at that time, European diseases were spreading without direct European involvement: the culture never had any interchange with Europeans aside from the odd explorer, but it didn't need to. By the time the US reached its former territory, it had thoroughly collapsed, such that some of its successor tribes didn't even know why the mounds it's now known for were built.

The agricultural traditions associated with both did survive, which was my main point, although some Mississippian descendants seem to have contributed to Plains Indian culture later on. I wanted to say something about Eastern Woodland agriculture (as made famous by Squanto et al.) too, but it didn't fit well into my post and Wikipedia didn't have a good summary. In practical terms it would have been basically Mississippian.