Final answer:
Arkansas is the state that has the Mississippi River as its eastern border, separating it from Tennessee and Mississippi.
Step-by-step explanation:
The state that has the Mississippi River form its eastern border, separating it from Tennessee and Mississippi, is Arkansas. The significance of the Mississippi River's boundaries can be traced back to historical negotiations and developments.
Explorations to determine the true source of the Mississippi River led to misconceptions, and it was not until 1832 that the headwaters were fully explored by non-Indians. Additionally, the river has served as a crucial boundary line for states' admissions to the Union, with states like Ohio, Indiana, and Illinois gaining admission along the river's northern banks.
The Mississippi River served as an essential demarcation during America's expansion, and was also a subject of contention due to the sectional differences tied to the institution of slavery in the United States.