The Porter–MacKenzie debate is a historiographical controversy in the field of Modern British and Imperial history. It focuses on the extent to which colonialism was an important influence within British culture during the 19th and 20th centuries. The debate was characterised by disagreement between the academic historians Bernard Porter and John MacKenzie, beginning in 2004. Porter argued that British imperial expansion during the era of New Imperialism had little effect on ordinary people in the United Kingdom, while MacKenzie argued that colonialism dominated British popular culture for much of the period.