Monopoly capitalism depends primarily on the private ownership of the means of production, including natural resources. Capitalist opposition to socialism is not only a matter of theory. In practice the private ownership of natural resources enables the owner to charge rent to any and all users. Natural resources are sharply limited and usually localized. As population grows, demand for living space is intensified and rents rise. It is not an accident that the stretches of "black earth", of copper, iron, petroleum, the precious metals, and the land occupied by Mexico City, London, New York and other population centers, poured a stream of wealth into the treasuries and augmented the power of their owners. Effects of the insertion into the Mexican Constitution of the provision making natural resources "the property of the Mexican people" have been far-reaching. One socialist country after another has written into its constitution a provision that its natural wealth is the inalienable heritage of its people. This provision has two important results: it establishes natural resources as part of the public sector of the national economy; it also limits the possibility of handing out concessions to foreign exploiters, private or public. During the opening years of the present century socialist parties and other forward looking organizations were demanding social ownership of natural resources, public utilities and other social means of production as the next logical step toward a more equitable distribution of wealth and income. There was a possibility that such revolutionary changes could be made under bourgeois law by exercising the right of eminent domain, upon the payment of reasonable compensation to former owners. At least in theory, the democratic majority in any bourgeois country could put an end to private enterprise capitalism and establish socialism by a constitutional amendment, legislative enactment, and a caretaker political apparatus to administer and supervise the transition. Socialist parties were making "reformist" demands for better working and living conditions and "revolutionary" demands for changes in property and class relationships. Increased productivity and growing affluence made it possible for a progressive bourgeois state to meet the reformist demands, establishing a welfare state legally and constitutionally. Under the bourgeois constitutions generally existing at the beginning of the present century, a popular majority could adopt necessary constitutional amendments, pass the necessary enabling laws and launch a program of socialist construction. Such a program was part of the thinking of European and other socialist leaders during the opening years of the present century. Inspired and encouraged by the successes of socialist construction in the Soviet Union and other socialist countries, middle of the road socialists proposed to move gradually and legally from capitalism to socialism.