Christianity and colonialism are associated with each other by some ideas, because of the service of Christianity, in its various denominations (namely Protestantism, Catholicism and Eastern Orthodoxy), as the state religion of the historical European colonial powers in which Christians likewise made up the majority. Through a variety of methods, Christian missionaries acted as the "religious arms" of the imperialist powers of Europe.

According to Edward E. Andrews, Associate Professor of Providence College Christian missionaries were initially portrayed as "visible saints, exemplars of ideal piety in a sea of persistent savagery". However, by the time the colonial era drew to a close in the later half of the 20th century, missionaries were critically viewed as "ideological shock troops for colonial invasion whose zealotry blinded them", colonialism's "agent, scribe and moral alibi". Meanwhile, "differing South Asian groups who enthusiastically embraced Christianity have been mocked as dupes of Western imperialists" and criticized as being "separatist minded by their initial communities."

In some regions, segments of a colony's population were forcibly converted from earlier belief systems to the Christian faith, which colonial regimes used to legitimize the suppression of adherents of other faiths, enslavement of colonial subjects, and exploitation of land and maritime resources. Christians and Christian institutions around the world, however, also participated in anti-colonial and decolonization movements and were themselves transformed in the process.

Christianity is associated by some with the impacts of colonialism because religion was a frequent justification among the motives of colonists. For example, Toyin Falola asserts that there were some missionaries who believed that "the agenda of colonialism in Africa was similar to that of Christianity". Falola cites Jan H. Boer of the Sudan United Mission as saying, "Colonialism is a form of imperialism based on a divine mandate and designed to bring liberation – spiritual, cultural, economic and political – by sharing the blessings of the Christ-inspired civilization of the West with a people suffering under satanic oppression, ignorance and disease, effected by a combination of political, economic and religious forces that cooperate under a regime seeking the benefit of both ruler and ruled."

Edward Andrews writes:

Historians have traditionally looked at Christian missionaries in one of two ways. The first church historians to catalogue missionary history provided hagiographic descriptions of their trials, successes, and sometimes even martyrdom. Missionaries were thus visible saints, exemplars of ideal piety in a sea of persistent savagery. However, by the middle of the twentieth century, an era marked by civil rights movements, anti-colonialism, and growing secularization, missionaries were viewed quite differently. Instead of godly martyrs, historians now described missionaries as arrogant and rapacious imperialists. Christianity became not a saving grace but a monolithic and aggressive force that missionaries imposed upon defiant natives. Indeed, missionaries were now understood as important agents in the ever-expanding nation-state, or "ideological shock troops for colonial invasion whose zealotry blinded them."

According to Lamin Sanneh, "Much of the standard Western scholarship on Christian missions proceeds by looking at the motives of individual missionaries and concludes by faulting the entire missionary enterprise as being part of the machinery of Western cultural imperialism." As an alternative to that view, Sanneh presents a different perspective arguing that "missions in the modern era have been far more, and far less, than the argument about motives customarily portrayed."

Michael Wood asserts that during the 16th century, it was almost impossible for the indigenous peoples to be considered human beings in their own right and that the conquistadors brought with them the baggage of "centuries of ethnocentrism, and Christian monotheism, which espoused one truth, one time and version of reality."