Across America, the rise of suburbia has lead to the replacement of small mom and pop grocers by large chain supermarkets. Not only are the small single store grocers going out of business, but also the slightly larger multi-store groups are closing as well. They are easily overrun by stores that stretch across the state or country. The development of these supermarkets can be explained largely by the increases in transportation technology and infrastructure.
Whereas in the earlier parts of the 20th century few Americans owned cars and were forced to walk to their grocers, now almost everyone is able to drive themselves. Proximity is less of an advantage and so supermarkets can take advantage of economies of scale to offer the same goods at lower prices. Moreover, increases in transportation technology have made it much easier to ship goods across the country, and even the world while they are still fresh.
This means that each grocer can purchase his wares from a variety of producers and stock his market with a much greater variety of items. Supermarkets, being larger than other grocery stores, can keep a larger variety of goods on hand. Things that smaller grocers can not afford to keep on the shelves if they do not sell quickly, can sit for months on the shelves of a larger grocery store without causing any problems to their bottom line. This variety also increases their appeal and together with the cheaper prices more than make up for their proximity.
Smaller grocery stores remain both in the cities, where congestion precludes the advantages of owning a car and in suburbia. In suburbia, smaller grocery stores tend to specialize in goods that are beyond the purview of supermarkets. Ethnic grocers, which import a variety of goods from one particular region of the world, remain viable, as do grocers specializing in healthier foods. These remain niche markets until they too become popular enough to be consolidated into supermarkets.