To put it simply, says Renalyn Mulato, the daughter of a Filipina immigrant married to a South Korean man, the key to multicultural happiness is love and understanding.

That may seem like a painfully obvious prerequisite for most marriages, but for many immigrants in South Korea, it isn’t always that easy.

South Korea has been grappling with shifting demographics that have left many middle-aged men cut adrift in a country that prizes marriage. As Korean women leave their hometowns for careers in the big cities, the men left behind are increasingly looking for brides from poorer Asian nations such as Vietnam, the Philippines, Cambodia, and Mongolia.

More than 100,000 women among South Korea’s 1.2-million foreign population are estimated to be foreign brides. This influx of foreigners has accelerated multiculturalism in Korea. But many of those marriages don’t turn out well. Part of the problem, say experts, is a lack of government oversight of agencies that locate foreign brides for Korean men. The result, say critics, is hundreds of unhappy marriages between middle-aged Korean men and young foreign women trying to escape poverty.

Korean men seeking to wed foreign brides are now required to take courses to prepare them for international unions.