Final answer:
The Spanish-American War marked the United States' emergence as a world power by demonstrating military strength, acquiring overseas territories, and establishing a presence in international trade, exemplified by the 'open door' policy with China.
Step-by-step explanation:
The Spanish-American War catapulted the United States into the position of a world power by allowing it to showcase its military might and by significantly altering the global balance of power. With the defeat of Spain, the U.S. gained control of several Spanish possessions such as Cuba, Puerto Rico, Guam, and the Philippines. This expansion was a clear move away from the country's previous isolationist stance, signaling its transition into an era of imperialism and strategic global influence.
Aside from military conquests, the United States also utilized its economic power, benefitted from the Industrial Revolution, to forge new international relationships, as seen with the 'open door' policy in China. The war underlined the American ambition of not just assisting Cuban independence, but also the broader goal of expanding its empire, evidenced by the acquisition of new territories and creating naval bases across the Pacific, extending reach to Asia.
Through these actions, the United States demonstrated its capability and intention to play a substantial role in international affairs, cementing its status as a formidable global power at the dawn of the twentieth century.