 Reasons that have been suggested for this change include the growing power of the nation state, socialism, and scientific rationalism, which provided alternatives to the social and intellectual aspects of religion.By the 1920s roughly half the population had a relationship with one of the Christian denominations.This level was maintained until the 1940s when it dipped to 40 per cent during Second World War, but it increased in the 1950s as a result of revivalist preaching campaigns, particularly the 1955 tour by Billy Graham, and returned to almost pre-war levels.