The answer is A: Because colonizing often involved violent conflicts.
Ever since the modern era, that, in this context, could be said to have started at the end of the 15th century when the Spanish conquerors arrived in America, there have been critics, from clerics to learned men and women, of the violence and injustices that this practice brought upon the natives who were invaded. Britain, after it begun its colonialist history in America, was not the exception and many were the ones that denounced this practice as unjust, a practice that, for Britain, goes from the 18th century to the end of the 20th century, that is, three centuries of invasion and violence.