In the last decades of the nineteenth century, after the Civil War, the United States pivoted from a profoundly isolationist approach to a distinct zeal for American expansion. The nation’s earlier isolationism originated from the deep scars left by the Civil War and its need to recover both economically and mentally from that event.

But as the industrial revolution changed the way the country worked and the American West reached its farthest point, American attitudes toward foreign expansion shifted. Businesses sought new markets to export their factory-built goods, oil, and tobacco products, as well as generous trade agreements to secure access to raw materials.

Frontier Thesis — an idea proposed by Fredrick Jackson Turner, which stated that the encounter of European traditions and a native wilderness was integral to the development of American democracy…. Open Door notes — the circular notes sent by Secretary of State Hay claiming that there should be “open doors” in China, allowing all countries equal and total access to all markets, ports, and…. Roosevelt Corollary — a statement by Theodore Roosevelt that the United States would use military force to act as an international police power and correct any chronic wrongdoing by any Latin American…. sphere of influence — the goal of foreign countries such as Japan, Russia, France, and Germany to carve out an area of the Chinese market that they could exploit through tariff and transportation….