In 1936, the Robinson-Patman Act was implemented as a way of preventing such larger chains from using this buying power to reap advantages over smaller stores, although the act was not well enforced and did not have much impact on the prevention of larger chains overtaking power in the markets.Supermarkets proliferated across Canada and the United States with the growth of automobile ownership and suburban development after World War II. Most North American supermarkets are located in suburban strip shopping centers as an anchor store along with other smaller retailers. They are generally regional rather than national in their company branding. Kroger is perhaps the most nationally oriented supermarket chain in the United States but it has preserved most of its regional brands, including Ralphs, City Market, King Soopers, Frys, Smiths, and QFC. In Canada, the largest such company is Loblaw, which operates stores under a variety of banners targeted to different segments and regions, including Fortinos, Zehrs, No Frills, the Real Canadian Superstore, and Loblaws, the foundation of the company. Sobeys is Canadas second largest supermarket with locations across the country, operating under many banners (Sobeys IGA in Quebec). Québecs first supermarket opened in 1934 in Montréal, under the banner Steinbergs.In the United Kingdom, self-service shopping took longer to become established. Even in 1947, there were just ten self-service shops in the country. In 1951, ex-US Navy sailor Patrick Galvani, son-in-law of Express Dairies chairman, made a pitch to the board to open a chain of supermarkets across the country.
The stores were a financial success and Saunders began to offer franchises. The Great Atlantic & Pacific Tea Company, which was established in 1859, was another successful early grocery store chain in Canada and the United States, and became common in North American cities in the 1920s. Early self-service grocery stores did not sell fresh meats or produce. Combination stores that sold perishable items were developed in the 1920s. The general trend since then has been to stock shelves at night so that customers, the following day, can obtain their own goods and bring them to the front of the store to pay for them. Although there is a higher risk of shoplifting, the costs of appropriate security measures ideally will be outweighed by reduced labor costs.Historically, there has been debate about the origin of the supermarket, with King Kullen and Ralphs of California having strong claims. Other contenders included Weingartens and Henke & Pillot. To end the debate, the Food Marketing Institute in conjunction with the Smithsonian Institution and with funding from H.J. Heinz, researched the issue. They defined the attributes of a supermarket as "self-service, separate product departments, discount pricing, marketing and volume selling".They determined that the first true supermarket in the United States was opened by a former Kroger employee, Michael J. Cullen, on 4 August 1930, inside a 6,000-square-foot (560 m2) former garage in Jamaica, Queens in New York City. The store, King Kullen, operated under the slogan "Pile it high. Sell it low."