Throughout the 20th century, government agencies increasingly regulated the use of private land in the United States. In particular, zoning spread across the country as the principal regulatory tool for land use control. Although many citizens and commentators welcomed this trend as a means to protect property interests and the neighborhood environment, zoning has faced increased criticism in recent decades. Among other charges, dissenters contend that zoning intrudes unwarrantedly into the realm of private property, interferes with the optimal market allocation of land uses, and works to segregate communities along racial and economic lines. The debate whether to pursue more regulation or to deregulate land development continues today. New York City Mayor Michael Bloomberg has proposed zoning law reforms to spur new housing construction. Gov. Mitt Romney (R-Mass.) has commissioned zoning reform studies to curb sprawl and encourage more diverse land uses. And Chicago Mayor Richard Daley has embarked on extensive zoning law revisions to update Chicago's 1957 zoning ordinance. In contexts such as these, lawmakers nationwide contemplate the appropriate level of government regulation.