'Which town was the gateway to the mississippi river and therefore necessary for the united state to acquire During the lewis and Clark expedition which statement best describe the Louisiana Purchase OPening the mississipi river to commerce was especially important to why was the missisip; river important to the united state in the late 1700 The northwest ordinance of 1787 addressed the issue of statehood in the northwest territory by One major was that the Lewis and Clark expedition affected American. business was that the explorers A main reason President Jefferson Sent Lewis eind Clark west in the early 1800 was to