Final answer:
Social Darwinism and the belief in American exceptionalism were key philosophies that motivated America's imperialist expansion during the Gilded Age, supported by the related concepts of Progressivism and missionary efforts.
Step-by-step explanation:
The philosophies that influenced America to become an imperialist power during the Gilded Age were predominantly Social Darwinism and the belief in American exceptionalism. Social Darwinism, with its premise of 'survival of the fittest', was applied to societies and nations, suggesting that strong countries like the United States were destined to dominate weaker ones. This idea, coupled with a sense of American exceptionalism—the belief that America had a unique mission to spread liberty and democracy—provided the ideological backing for imperialism during this period.
Progressivism also played a role, as many reformers who sought domestic democratic changes saw expansion as a means to apply these ideals internationally. Additionally, religious organizations contributed to imperialistic desires by linking their Christian missionary efforts with the spread of an 'American' way of life.
It is important to note that while Social Darwinism and American exceptionalism were major influences, other factors like economic interests, strategic concerns, and global competition were also significant in America's turn toward empire building.