Josiah Strong in The Spanish-American War
Josiah Strong (1847–1916) was a clergyman and writer who preached of the saving power of Protestant religious values. He's best known for his book, Our Country: Its Possible Future and Its Present Crisis, in which he urged Anglo-Saxons to "civilize and Christianize" the American West.
More specifically, Strong called for Anglo-Saxons to spread their superior institutions and values to "inferior races." Civilizing "savages," he said, would be both good for the uncivilized peoples and for the American economy.
Many of those in favor of global expansion in the late-19th century found inspiration in this work.