What development helped improve trade in the Midwest? Eli Whitney's cotton gin George Stephenson's locomotive Robert Fulton's steamboat Thomas Jefferson's plow

Robert Fulton's steamboat

Explanation:

roosevelt believed that in light of the country's recent military successes, it was unnecessary to use force to achieve foreign policy goals, so long as the military could threaten force. this belief, and his strategy of “speaking softly and carrying a big stick,” shaped much of roosevelt's foreign policy.