The Mississippi River is the largest and longest river in North America and, as a result, became the main geographical border between the United States and Allied States. Due to its location and prime navigable waterways, it is a critical resource for commerce, industry, and most other areas vital to both nations' economic health and survivability.
As a result of the anarchy, mass confusion, and eventual fragmentation within the United States that occurred in the wake of the September attacks, United Nations peacekeepers were apparently emplaced along the Mississippi River in an effort to stabilize the volatile new border between the two Americas.
The river is known as the "Blue Line" in recognition of the light blue helmets that UN peacekeepers wear while performing their mission.
