When the Kingdom of Italy annexed Rome in 1870, the city had a population of about 225,000. Less than half the city within the walls was built up in 1881 when the population recorded was 275,000. This increased to 600,000 by the eve of World War I. The Fascist regime of Mussolini tried to block an excessive demographic rise of the city but failed to prevent it from reaching one million people by the early 1930s. Population growth continued after the Second World War, helped by a post-war economic boom. A construction boom also created many suburbs during the 1950s and 1960s.