Final answer:
The Mississippi River and its tributaries were the key physical characteristics of Louisiana that provided Europeans, and later Americans, access to the interior of North America. This network of waterways was instrumental in the expansion and economic exploitation of the continent following the Louisiana Purchase in 1803.
Step-by-step explanation:
The physical characteristic of Louisiana that gave Europeans access to the interior of North America was its network of rivers and waterways, notably the Mississippi River. This river system proved indispensable to the European explorers and settlers, as it allowed for the transportation of goods and people deep into the continent. The pursuit of economic opportunities such as the fur trade and fishing, along with the aim of establishing new territories for European powers, was greatly facilitated by these waterways. When President Thomas Jefferson purchased the Louisiana Territory from France in 1803, this access was a crucial factor that led to the expansion of the United States and its influence across North America.
The major waterways, including the Mississippi River and its tributaries, were the gateway not just for trade but also for exploration. The purchase of the Louisiana Territory presented the United States with the opportunity to explore, map, and eventually exert control over this vast expanse of land. The Louisiana Purchase itself was a significant event, as it doubled the size of the country and highlighted the importance of the water routes for interior access and the potential for American commerce and influence, especially following Jefferson's commissioned expedition of Lewis and Clark's Corps of Discovery.