Final answer:
Imperialists considered themselves superior primarily in racial terms, believing that they were biologically and culturally destined to rule over other races. This belief justified the spread of their customs, religion, and governance through colonization, exemplified by ideologies such as the Anglo-Saxon superiority promoted by figures like Josiah Strong and works like Kipling's "The White Man's Burden".
Step-by-step explanation:
The type of superiority that imperialists considered themselves to have was primarily racial superiority. This belief was rooted in the idea that certain races were biologically and culturally superior, and thereby destined to rule over others. Prominent at the time, figures like Josiah Strong promoted the notion of Anglo-Saxon superiority, arguing that it was America's moral responsibility to spread liberty and Christianity. This ideology was part of the larger imperialistic view that European (and later, American) colonization brought with it the 'benefits of civilization' to the conquered peoples, as reflected in Rudyard Kipling's "The White Man's Burden". Additionally, the Europeans and the Japanese during their respective imperialistic expansions believed that they were improving societies by enforcing their customs, religious beliefs, and governance styles upon the peoples they colonized.