The Southern Railway in the United Kingdom, which existed between 1923 and 1948, was geographically the smallest of the four railway systems created in the Grouping ordered by the Railways Act 1921. Confined to the south of England, it owned no track north of London. In the area south and south-east of London it had a virtual monopoly, while some of its lines to the south-west were in competition with the Great Western Railway. The war-devastated company was nationalised, along with the rest of the British railway network, in 1948, into British Railways, as the Southern Region. Many of its lines in London and Kent had been damaged during the war and much of the rolling stock was either damaged or badly in need of replacement. At the time of nationalisation the Southern had started a vigorous programme of rebuilding and renewal.