Final answer:
The best example of America's economic motive for imperialism was opening foreign markets to ease domestic economic tensions. The pursuit of new consumers overseas, especially in China and Latin America, directly aligned with the United States' strategy of economic expansionism to maintain its industrial growth and global influence.
Step-by-step explanation:
The best example of an economic motive behind America's increasing expansionism and imperialism in the years leading up to World War I is A) Imperialism opened foreign markets for American agricultural and industrial products, easing economic tensions at home. This response reflects the United States' shift towards using its economic clout to build an empire. Industrialization had given American businesses the upper hand in producing goods more efficiently, and by seeking new markets, the U.S. could ensure a way to dispose excess production while continuing to grow economically.
Moreover, the pursuit of an open door policy with China aimed to guarantee American products would find new consumers. Additionally, the economic domination of Latin American countries by U.S. investors shows how expansionism extended over supposedly independent nations, leveraging them as sources of raw materials and as markets for finished goods.
Finally, the transition from a nation adhering to isolationism to one actively participating in imperialism was influenced by the need to compete with European nations who sought territories for resources and markets, fueled also by fears of America's growing economic might. Thus, gaining new markets for American goods was a primary driver of its imperialism strategy.