Final answer:
The state with the Mississippi River forming its eastern border and including the Des Moines, Missouri, and Cedar Rivers is Iowa. The river has deep historical and geographical significance in the U.S.
Step-by-step explanation:
The state with the Mississippi River forming its eastern border and containing the Des Moines River, Missouri River, and the Cedar River is Iowa. The Mississippi River's boundary is significant, not only for Iowa but also in the context of American history. It has served as a vital waterway for commerce, exploration, and geopolitical boundaries since the colonial era.
For instance, the boundary between the Mississippi River and the 49th parallel was uncertain due to the misconception that the source of the Mississippi River lay further north than it actually does. It was once believed that the Mississippi might offer a potential Northwest Passage for commerce.
This river has also been the subject of extensive geological study, such as examining its previous channels, and it plays a critical role in the history of territorial expansion and debate, such as during the admission of Missouri into the Union.