why might location have been important to the power and wealth of the mississippian culture?

Depends if you mean the Native mound-builders or the U.S. slaver-ruled nation from 1789-1865.

I don't know much about the former, a little about the latter. For that, being near the river allowed river-shipping of cotton and other agricultural products, and the slaves forced to produce them.

In the U.S. slaver-era economy, the most important physical assets for a successful exploiter were land, slaves to work it, and products. Two of those could be shipped by boat, and the wealth they represented accumulated in clumps along the Mississippi.

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[SEE: Cultural implications -- derivation of U.S.-used colloquialism "Sold down the river."]

The most advanced and prosperous civilizations developed in the most fertile river valleys particularly on or around their flood plains. The Nile delta culture was one of the most famous.

Such areas allow large civilizations to grow on reliable agricultural land. Typically they do not need to constantly move as they deplete the soil where they farm and graze. The rivers have created fertile land and replenish it regularly.

That's why the earliest advanced civilizations were at the Nile, Yangtze, Indus, and Tigris-Euphrates valleys.

The Mississippian cultures had similar conditions where they developed.

https://images.search.yahoo.com/search/images;_ylt...

Becuase, it's jsut that way