in the late 1990s set it against major supermarket chains in both the United States and Canada. Studies have typically found that Walmart's prices are significantly lower than those of their competitors, and that Walmart's presence is associated with lower food prices for households. Comparisons of performance metrics such as sales per square foot suggest that supermarkets in direct competition with Walmart Supercenters show significant decreases in profit margins, an effect that is strongest in the case of unionized competitors. Between 2000 and 2010, Walmart's entry into new areas often lowered local food prices at other stores. However, recent studies have not found the same effect, suggesting that retailers may have changed their competitive strategies. While the idea that Walmart destroys small businesses is widely assumed to be true, research so far suggests that Walmart superstores have little effect on smaller retailers such as "Mom and Pop" businesses. Differences in impact appear to be specific to the goods sold. Small retailers may experience difficulty if they rely on selling products identical to those at Walmart or if they try to sell at lower prices. Dollar stores such as Family Dollar and Dollar General have been able to find a small niche market and compete successfully against Walmart. In 2004, Walmart responded by testing its own dollar store concept, a subsection of some stores called "Pennies-n-Cents". Walmart also had to face fierce competition in some foreign markets. For example, in Germany it had captured just 2 percent of the German food market following its entry into the market in 1997 and remained "a secondary player" behind Aldi with 19 percent. Walmart continues to do well in the UK, where its Asda subsidiary is the second-largest retailer. In May 2006, after entering the South Korean market in 1998, Walmart sold all 16 of its South Korean outlets to Shinsegae, a local retailer, for . Shinsegae re-branded the Walmarts as E-mart stores. Walmart struggled to export its brand elsewhere as it rigidly tried to reproduce its model overseas. In China, Walmart hopes to succeed by adapting and doing things preferable to Chinese citizens. For example, it found that Chinese consumers preferred to select their own live fish and seafood; stores began displaying the meat uncovered and installed fish tanks, leading to higher sales. Customer base In the United States, Walmart's early growth occurred in the Southeast and lower Midwest. More recently, Walmart has