BUSAN, South Korea — Last September, a 55-year-old man lit some scrap paper on fire and threw it into a Seoul subway car as he left the train. He had just been cursed at and kicked by senior citizens for sitting in a seat designated for “the elderly and the infirm.”

The man, whom we know only by his surname of Kim, was sentenced on Jan. 14 by a Seoul court to one year and six months in prison. One news article reporting the results of his trial garnered more than 1,000 comments in just one day, most of which were from sympathetic younger people complaining about being forced to give up their seats on the subway to senior citizens. Mr. Kim is hardly young, but his frustration resonated with the younger generations.

The Seoul subway’s designated-seating section has become a curious backdrop of intergenerational conflict in South Korea. In the 40 years or so since full-scale industrialization began, the social divide between generations has widened. Senior citizens grew up during Japanese occupation and the Korean War, and lived through the era of breakneck economic growth that followed, building a modern country from the ground up in just a few decades, most of the time under a military dictatorship. Most younger South Koreans have come of age in a time of relative affluence and freedom, and like many younger people in East Asia, have gradually become more independent-minded than their elders and less attached to the traditional Confucian values that have been the basis of Korean society for centuries.

In recent years, South Korea’s economic woes have put strain on both groups, and frustrations are high. Older South Koreans are finding themselves financially unprepared for retirement, while younger people can’t find jobs. The Seoul subway is a rare place where the generations cross paths — and the intergenerational tensions are playing out in the crowded trains.