BUPYEONG, South Korea — When sales at his clothing shop began sliding several years ago, In Tae-yeon first attributed the drop to a bad economy. But he said he soon realized that the real culprit was something else: hypermarkets crowding into busy commercial districts, attracting shoppers with their easy-to-use parking lots, flashy signs and cutthroat discounts and, as Mr. In put it, “sucking the life out of small-business men like me, like vampires.”


The arrival of hypermarkets — vast department stores that also contain supermarkets — is relatively new in South Korea; a few began opening two decades ago. But they are unique in the country because most are owned by chaebol, the family-controlled conglomerates whose dominance in large and increasingly diverse swaths of the economy is prompting many in South Korea to refer to the country as the Republic of Chaebol.


Rapidly expanding nationwide chains of hypermarkets, supermarkets and 24-hour-a-day convenience stores are the latest and perhaps most visible examples of the penchant among the chaebol for seemingly relentless growth. Total revenue at hypermarkets grew to 33.7 trillion won, or $30.3 billion, in 2010 from 23.7 trillion won in 2005, according to Statistics Korea, the national statistical agency. During the same period, sales at traditional markets, where individual dealers sell products as varied as manufactured goods, meat and farm produce, declined to 24 trillion won from 32.7 trillion won, according to the government’s Agency for Traditional Market Administration.


So when owners of small stores, like Mr. In, began pushing back, picketing hypermarkets and lobbying lawmakers, they started a South Korean version of the “We are the 99 percent” campaign — a movement in support of what is called “economic democratization.”


The chaebol are widely credited with leading South Korea’s economic growth, exporting goods as diverse as computer chips, cellphones, cars and ships. The number of subsidiaries of the top 30 conglomerates jumped to 1,150 last year from 731 in 2007. The five biggest chaebol — Samsung, Hyundai Motor, SK, LG and Lotte — generated 653 trillion won in sales in 2010, the equivalent of 55.7 percent of South Korea’s gross domestic product.


But at home, the sprawling corporate empires are also seen as predators — so much that protecting smaller businesses from them has become a prominent slogan for both the governing party and the opposition before the December presidential election, which is approaching amid growing discontent about a widening gap between rich and poor. The anti-chaebol rallying cry is a reference to the country’s 1948 Constitution, which requires the state to “prevent the domination of the market and the abuse of economic power and to democratize the economy through harmony among the economic agents.”


For several years, store owners in the traditional shopping street where Mr. In keeps his shop have suffered declining sales because of competition with three hypermarkets and a department store, all within about two kilometers, or 1.2 miles, and all owned by Lotte.


“We only ask chaebol to let us live together with them,” Mr. In, now the leader of a nationwide network of 5,000 independent shop owners, said in an interview at his shop in Bupyeong, a bustling town east of Seoul. “Currently they are behaving like giant serpents gobbling up everything.”


Other countries have found their mom-and-pop retailers squeezed out by hypermarkets, like Wal-Mart in the United States or Tesco in Britain, but to understand how the chaebol operate is to understand how the South Korean economy works.


A typical chaebol comprises dozens of subsidiaries that its chairman controls through a web of cross-shareholdings. Armies of subcontractors depend on the chaebol through patron-client relationships.