Before the 1950s, the department store held an eminent place in both Canada and Australia, during both the Great Depression and World War II. Since then, they have suffered from strong competition from specialist stores. Most recently the competition has intensified with the advent of larger-scale superstores (Jones et al. 1994; Merrilees and Miller 1997). Competition was not the only reason for the department stores' weakening strength; the changing structure of cities also affected them. The compact and centralized 19th century city with its mass transit lines converging on the downtown was a perfect environment for department store growth. But as residents moved out of the downtown areas to the suburbs, the large, downtown department stores became inconvenient and lost business to the newer suburban shopping malls. In 2003, U.S. department store sales were surpassed by big-box store sales for the first time (though some stores may be classified as "big box" by physical layout and "department store" by merchandise).