Final answer:
Christianity reached the British Isles through Roman conquest and expansion, with the Roman Empire becoming officially Christian by 380 CE under Emperor Theodosius I. The faith spread throughout the empire, notably influencing regions in North Africa and the Kingdom of Aksum through figures like Frumentius.
Step-by-step explanation:
Christianity was brought to the British Isles after 55 BCE and was present until at least 407 CE largely due to the Roman conquest and presence in the region. After the Romans conquered the region of Israel, Jesus of Nazareth began preaching and upon his crucifixion, his disciples, notably Paul, continued to spread his teachings. The Romans sometimes persecuted Christians, but despite this, the religion attracted a large following, especially among slaves, due to its message of salvation, forgiveness, and eternal life. The religion officially spread throughout the Roman Empire, including into the British Isles, becoming the empire's official religion by 380 CE under Emperor Theodosius I.
The spread of Christianity was not limited to Europe, as it quickly reached North Africa and into communities like the School of Alexandria. From Alexandria, Christianity was further disseminated southward along the Nile into Upper Egypt. Similar patterns occurred elsewhere, such as the Christian Kingdom of Aksum where the missionary Frumentius played a pivotal role in the conversion of Aksumite royalty and the growth of Christianity in Ethiopia.