Final answer:
The biggest impact on the disappearance of the Mississippian culture was the introduction of diseases by the Spanish, against which the native populations had no immunity, resulting in widespread devastation.
Step-by-step explanation:
The disappearance of the Mississippian culture is largely attributed to the diseases brought by the Spanish, such as smallpox. These diseases had a catastrophic impact on Native Americans, including the Mississippians, because they had no immunity to European diseases. Smallpox and other diseases swept through the Americas with deadly efficiency, decimating native populations.
Records indicate that by the time the first Spanish explorers arrived, the once large Mississippian chiefdoms had already begun to collapse and were replaced by smaller communities that continued to display cultural traditions developed centuries earlier. However, the introduction of European diseases exacerbated the decline and had profound consequences on the native populations. The disruption of established communities and trade networks, coupled with the loss of a significant portion of the population due to disease, was instrumental in the cultural shift away from the Mississippian tradition.