SEOUL, South Korea — Thousands of years of deeply complicated history bubbled beneath the surface images of handshakes and flashing cameras Monday at the first formal meeting of Japanese and South Korean leaders in 3½ years.
The two Asian heavyweights' relationship is so unique, so vexing, that the major accomplishment of the summit, which included a three-way meeting Sunday with China's premier, was simply Japanese Prime Minister Shinzo Abe and South Korean President Park Geun-hye rising, for now, above past disputes and agreeing to meet again.
More talk, in a cordial, formal setting, is no small result for these two often bickering neighbors.
Here then is a look at five things that unite and divide Japan and South Korea:
A LONG, OFTEN UNEASY HISTORY
Both Japan and the Korean Peninsula have benefited from centuries of exchanges of people and ideas.
Much of the contact, however, has been bloody. Many Koreans are knowledgeable about aspects of Japanese invasions of the peninsula in the late 16th century that were repulsed only after massive slaughter and devastation.
Bitterness also lingers over what is seen as Japan's whitewashing of its colonization of Korea in the early 20th century, when Japan enslaved many Koreans in military brothels — a dwindling number of whom gather for weekly protests in front of the Japanese Embassy in Seoul — and Japanese mines and factories.
In Japan, the history dispute has sparked occasional fringe protests against Japan's 500,000-strong ethnic Korean population — some third- or fourth-generation descendants of those who came or were brought to Japan as laborers during the colonial era.
Tokyo says all wartime compensation issues have been settled under a 1965 normalization treaty.
RELATED, BUT VERY DIFFERENT, CULTURES
Japan has borrowed much from China and Korea over the centuries: language and religious and cultural aspects, for example. Envoys from the countries regularly traveled back and forth, stoking interest and curiosity, and even now a mutual fascination lingers.
About 2.5 million South Koreans travelled to Japan last year, while 2.3 million Japanese visited South Korea, according to South Korea's Korea Tourism Organization.
Japanese enthusiasts travel to Seoul for K-Pop concerts and to take tours of the neighborhoods of their favorite South Korean TV stars.
After South Korea began lifting its ban on Japanese pop culture in the late 1990s, Japanese movies, cartoons and other pop culture flooded in. The countries also co-hosted the soccer World Cup in 2002.
The history spat, however, has cast a shadow at times. South Korean stars who were once common on Japanese commercials have largely disappeared from them, and Japanese TV stations have cut back on Korean programming, partly over protests when the shows were broadcast.
ARGUMENTS OVER LAND — AND SEA
The countries contest barren volcanic outcroppings located in fishing rich waters roughly halfway between South Korea and Japan. They are occupied by Seoul but claimed by Tokyo.
Japan, which calls the rocks Takeshima, says it has historical evidence backing its sovereignty since at least the 17th century. South Korea has countered that it has far older historical evidence that the islets it calls Dokdo are theirs.
The countries also bicker over what to call the body of water between them. Japan, and much of the world, refers to it as the Sea of Japan. South Korea insists on its name for the water: the East Sea.
STAYING SAFE IN A TOUGH NEIGHBORHOOD
Both countries are strong U.S. allies and the bulwark of U.S. defense efforts in the region. Some 80,000 U.S. troops are stationed in the countries, both to combat possible North Korean provocations and to send a signal to a rising China as it tests its territorial claims and U.S. military power in Asia.
Tokyo and Seoul are also worried about North Korea's nuclear bomb and missile ambitions and are part of now-stalled six-nation North Korean nuclear disarmament talks.
After a South Korea-Japan intelligence-sharing pact on North Korea collapsed at the last minute following a backlash in South Korea in 2012, the countries signed a three-way pact with Washington to share Pyongyang-related intelligence.
ECONOMIC TIES — AND COMPETITION
Japan and South Korea are major commercial partners, even as they jockey for markets. South Korea was Japan's No. 3 trading partner last year and vice versa.
Japan was passed by China for the world's second-largest economy several years ago, but its people are far more affluent on average, and it's a manufacturing and technology powerhouse with globally recognized brands.
Despite a decline in population and two decades of domestic economic malaise, Japan's prowess in fields from robotics to architecture and pop culture means it is a role model for many South Koreans.
The mobile and Internet startup scene in South Korea, one of the world's most wired places, meanwhile, has attracted Japanese venture capitalists.
There is also interest in Seoul in a major trade initiative that includes Japan and the United States: the Trans-Pacific Partnership, a yet-to-be ratified free trade arrangement among a dozen nations.
AP writer Hyung-jin Kim in Seoul contributed to this report.
Foster Klug is AP's Seoul bureau chief. Follow him on Twitter at twitter/apklug