This story was updated on Dec 28, 2015.
Japan and South Korea reached a landmark agreement over wartime sex slavery on Monday (Dec 28).
Japan will draw on its government budget to contribute about one billion yen ($8.3 million) to a fund that will help the former "comfort women", and work with South Korea to run a programme to restore their honour and dignity.
Japanese Prime Minister Shinzo Abe also expressed "anew his most sincere apologies and remorse" to the women, said Japanese Foreign Minister Fumio Kishida.
We revisit the emotive issue, which has caused much ill-will between Japan and its neighbours in the post-war decades.
Some 200,000 women, mostly from Korea but also from China, Indonesia, the Philippines and Taiwan, were forced to serve Japanese soldiers during the war in brothels. At least 10 per cent of the women were Japanese.
The term "comfort women" entered mainstream consciousness when a group of former sex slaves from South Korea broke their silence about what had happened to them during World War II.
They brought their case to a Tokyo court to demand compensation and an official apology.
The lawsuit forced the Japanese government to acknowledge the existence of comfort women, but the official stance was that officials did not know how the women were recruited and that there were no official documents to prove official involvement.
Japanese historian Yoshiaki Yoshimi, fed up with the Japanese government's denials of complicity in the forced recruitment of comfort women and the setting up of brothels, went to the Defence Agency's library to look for proof. After two days combing through official documents from the 1930s, he discovered a trove of papers documenting the military's direct role in managing the brothels, including documents that carried the personal seals of high-ranking Imperial Army officers.
His work forced an embarrassed Japanese government to acknowledge the historical truth and drop its longstanding claim that only private businessmen ran the brothels.
Professor Yoshimi, who teaches at Tokyo's Chuo University, is also the head of the private Centre for Research and Documentation on Japan's War Responsibility.
Prof Yoshimi's findings led to the historic Kono statement. Issued by the government and named after its chief spokesman and then ruling party president Yohei Kono, the statement acknowledged official complicity in the abduction and coercion of women from across Asia into a chain of wartime brothels. It also expressed "sincere apologies and remorse".
As a result of his work, and the Kono statement, by 1997, all seven government-approved junior high school textbooks included sections about Japan's wartime practice of sex slavery.
But the statement also sparked an immediate backlash from the nationalist right, led by Mr Shinzo Abe, then a young and little-known lawmaker in the Liberal Democratic Party. He led a lobby to rescind the statement.
A Straits Times report said that at least five comfort houses were located in Singapore. They included Pulau Bukom, Sentosa Island, shophouses along Cairnhill Road and Tanjong Katong Road, as well as the Chin Kang Huay Kuan clan association building at Bukit Pasoh.
The story quoted former Cabinet minister Othman Wok as saying that the shophouses along Tanjong Katong Road between Wilkinson and Goodman roads were surrounded by "wooden walls so no one could look inside". He added: "There were Indonesian and Korean girls in white uniforms like nurses. People told me this place was for prostitutes."
The Asian Women's Fund was set up by Prime Minister Tomiichi Murayama's left-leaning government to help former comfort women.
Many of the victims rejected the fund's aid because it did not come from the government. Although it was administered by the government, the money was donated by private businesses. The fund struggled to meet fund-raising targets. By 1996, it had raised only 144.5 million yen, far short of the 1 billion yen target.
The fund paid each woman about 2 million yen.
Mr Murayama also solemnly apologised, in a nationally televised speech marking the 50th anniversary of the end of World War II, for Japanese atrocities during the war. Later, during a citizens peace forum, he also apologised to comfort women.
However, his apology was not well received by regional neighbours as different factions in his ruling coalition issued separate statements which seem to both acknowledge and ignore the role of Japanese aggression in World War II.
The fund was closed down in 2007 under Prime Minister Shinzo Abe after only 285 former comfort women accepted money.
A Japanese court ruled in a landmark judgment that the Japanese government has to pay 300,000 yen in damages to each of three South Korean women. They were part of a group of 10 plaintiffs (the other seven were forced labourers) who had sued the government for 564 million yen in damages. The decision was seen as a symbolic victory for the women.
However, the court's ruling was overturned later in 2001 by Hiroshima's High Court.
Prime Minister Shinzo Abe said that there were no official documents to prove that the military was directly involved in forcing women into sexual slavery or the setting up of brothels. His stance undermined the Kono statement and sparked outrage in Asia.
The international backlash was so strong - with criticism from China, South Korea and the United States - that Mr Abe was forced to declare that the 1993 apology still stands and he also proffered another apology although he stopped short of admitting that the military was involved in sex slavery.
The Associate Press reported that Japan's practice of enslaving women to provide sex for its troops was continued post-war in Japan itself. A string of comfort women stations was set up to cater to American troops which had poured into occupied Japan.
Even more shocking, there was evidence that the US authorities were aware that women were being forcibly recruited, but turned a blind eye. The system was in operation from August 1945 to spring of 1946 when General Douglas MacArthur shut it down.
In the same year, history professor Hirofumi Hayashi of Kanto Gakuin University said he had found papers from the 1946-1948 Tokyo trials of war criminals which offered new proof that the Japanese army had forced Asian women into sexual slavery.
A Japanese lieutenant had testified in the trial that the army forced women into slavery in Indonesia. Prof Hayashi added that according to the documentation, "the army forced local girls into brothels. It says that it was in retaliation against local villagers who attacked the Japanese force. The army killed 40 villagers and put six of their daughters into brothels. It says one of the six agreed to the demands that she work at a brothel, while five others refused but were forced".
Despite the documentation and facts, Japan's continued refusal to offer an unconditional official apology still rankled with its neighbours.
The issue of comfort women has even disrupted the traditionally close relationship between the United States and Japan. Statues commemorating comfort women have been unveiled in the US and drawn protests in Japan from the right-wing demographic.
There has also been controversial statements by senior Japanese political figures about comfort women. Osaka's mayor Toru Hashimoto, for example, drew fire for stating that the forced recruitment of comfort women was "necessary". He was forced to apologise.
In April, China released previously confidential Japanese wartime documents which offered further lurid proof of Japanese atrocities in China. The 89 documents from archives in Jilin province included letters written by Japanese soldiers, newspaper articles as well as military files. The papers described in gruesome details rapes of ordinary women and children, as well as the conditions at comfort stations.
In November, South Korean President Park Geun Hye and Japanese Prime Minister Shinzo Abe held the first bilateral summit between the countries in more than three years, agreeing to expedite a resolution of the issue.
This led to an agreement on Dec 28, 2015 which would be "final and irreversible" if Japan fulfils its responsibilities, South Korean Foreign Minister Yun Byung-Se said.