The changing economic and social conditions of the 19th century led to a division between neo-classical and social (or welfare) liberals, who while agreeing on the importance of individual liberty differed on the role of the state. Neo-classical liberals, who called themselves "true liberals", saw Locke's "Second Treatise" as the best guide and emphasised "limited government" while social liberals supported government regulation and the welfare state. Herbert Spencer in Britain and William Graham Sumner were the leading neo-classical liberal theorists of the 19th century. The evolution from classical to social/welfare liberalism is for example reflected in Britain in the evolution of the thought of John Maynard Keynes.