And while Europe has made major efforts to resolve the question of ownership of works collected by the Nazis and subsequently pillaged during the second world war, notably by the invading Russian army, little has been done in East Asia to track down treasures that were the victors' spoils.
"The situation is very complicated," says Toshiyuki Kono, a law professor at the University of Kyoto and a member of a Unesco team examining how to deal with objects whose provenance is unclear.
In Europe, ownership disputes between museums, middle-men and people claiming to be the descendants of the owners of items - many of whom died in Nazi concentration camps - have reached the courts. In Japan, however, it is harder to determine ownership, even if an item is located.
"There is no proof that the Japanese government or the military arranged to systematically take art to Japan, so we have to assume that some of it was done through legitimate transactions," says Kono.
"Some deals were clean; others were different shades of grey - all the way down to black," he adds. The problem will be determining which items were purchased on the market and which looted.
Complicating the matter further was the recognition in 1910 by Great Britain and the United States of Japan's annexation of the Korean peninsula. This allowed Japan to act within international law when moving cultural artefacts around its territory.
"We do not know when most of these items came to Japan and the trade in cultural objects is very long and difficult to trace," says Kono. "That makes it almost impossible to apply the rules set up to resolve the problem of 'Holocaust art' to the East Asia situation."
Invaders and more peaceful visitors returned to Japan with items as far back as the Asuka Period, the 160 years before 710 CE, as well as the invasions of the 1590s under the shogun Toyotomi Hideyoshi.
The first Japanese archaeologists went to Korea in 1900 to survey sites, but the digging expanded rapidly with annexation 10 years later. The Japanese were particularly interested in Korea's famous green celadon pottery, which local people took for granted, according to Cheeyun Kwon, an art historian at Seoul National University.
The Imperial Palace is home to
thousands of treasures
For example, Hirobumi Ito, a former Japanese prime minister and later an adviser to the puppet Korean king, amassed a large collection of celadon, says Kwon.
"He gave these as gifts to members of the Meiji government and the emperor, with Japanese records showing this."
An almost frenzied excavation of tombs - including royal tombs - led to works ending up on the black market.
Today, research by the Korean government suggests that 29,000 items are held in galleries and museums. In total, some 300,000 works are believed to be in Japan, meaning the vast majority are in the hands of private collectors who are unlikely to want the government to know about them as they may have been purchased on the black market and bypassed tax laws.
In other cases, archaeologists know exactly where individual items ended up.
Tenri University, in the central Japan city of Nara, is in possession of a painting known as the Mongyu Towondo (Dream of Playing in a Peach Orchard) that dates back to the 15th century. The work was bequeathed to the university in 1953 by the family of its founder, but had been in the Shimazu family of southern Japan since Hideyoshi's invasions. The question remains; was it purchased or pillaged?
A spokesman for the Imperial Household Agency confirmed that the Museum of the Imperial Collection has a large Korean collection, but was unable to comment on the provenance of any of the works or those lining the walls of the Imperial Palace.
The problem of looting of cultural treasures is not limited to the last century, however. There is still a very active black market for artefacts that are stolen from temples and monasteries in South Korea, according to Hyung Il Pai, an associate professor in the history department of the University of California, Santa Barbara.
Japan is still reaping the legacy
of its imperial past
"Monks have drawn up a list of items, especially folk art, that have been stolen because there are no guards or security at remote temples or monasteries," she said. "The thieves simply break off the lock and cut pictures out of their frames and are gone into the forests by the time the police arrive the next day.
"They appear usually on the black market in Hong Kong, getting there via northern China," she said, adding that a colleague who had visited the national museum in North Korea said the entire collection was made up of replicas because the originals had been sold off for hard currency.
Relations between Seoul and Tokyo have improved markedly in recent years, as both sides try to move beyond Japan's sometimes brutal colonisation of the peninsula, although there remains a degree of anger in South Korea that more efforts have not been made to locate and return looted items.
Part of the problem, according to Yoko Hayashi, an assistant professor at Japan's Shobi University, is the failure to recognise by some private collectors that the real value of their hidden collections goes beyond a price.
Relations between South Korea
and Japan have improved
"There is a lack of perception of these items as cultural property that should be commonly held," she said. "Japanese people and the government do not understand that even though they are privately owned, they do not belong to them; they belong to humankind."
The Japanese government's position is that the 1965 normalisation treaty between Seoul and Tokyo has settled all claims on cultural properties and that it is unable to force items that are in private hands to be returned.
And while Japanese individuals have returned items to Korea - a collector of roof tiles returned 1082 items from his collection in 1987 - a lot more important art works are simply unaccounted for.
"We should not take as the starting point that all the items are of questionable provenance," says Kono.
"But it there are some in a grey area when we have to apply a moral principle. We must make these people collectors that by voluntarily returning these pieces, it will help many people and the culture of the world."