In 43 AD, the fourth emperor of Imperial Rome, Tiberius Claudius Drusus, organized his military and invaded Britain. The purpose of this paper is to investigate the legitimate reasons for The Invasion of Britain led by Claudius. Before the invasion, his had an unfortunate life. He was physically distorted, so no one gave him an official position. However, one day, something unimaginable happened. He found himself selected by the Praetorian Guard to be the new emperor of Roma. Many scholars generally agree Claudius was eager to overcome his physical disabilities and low expectations to secure his position as new Emperor in Rome by military success in Britain. Although his personal motivation was understandable, it was not sufficient enough for Imperial Rome to legitimize the invasion of Britain. It is important to separate personal reasons and official reasons. A significant part of this research was library based. In this paper, I will focus on three possible reasons Claudius used to legitimatize the invasion of Britain: 1) Human Rights: To salvage refugees from Britain, 2) Social Welfare: To distribute land and resources for military veterans as part of a social welfare program, and 3) Natural Slave Theory: To apply ancient Greek philosophy by Plato and Aristotle. Because primary sources are limited during the first century, I applied an interdisciplinary view to analyze texts to complete my study.