Describe the united states' movement from isolationism to expansion-mindedness in the final decades of the nineteenth century. what ideas and philosophies underpinned this transformation?

Manifest Destiny and Industrialization--the idea that Americans were destined to expand turned the US to a global expansion. Also a want for more resources and markets became important for businesses. 

The US would begin expanding in particular to the Pacific to create a modern nation with global connection. Reformers expanded cultural ideas and businesses gained resources. The military also expanded as the navy grew with new bases on many of the newly obtained islands.