TOKYO - Key questions and answers about Tokyo's Yasukuni war shrine, which came back into focus on Thursday when Prime Minister Shinzo Abe became the 15th post-war prime minister to visit, enraging Japan's neighbours.
Q. What is Yasukuni Shrine?
A. Yasukuni was founded under orders from then-emperor Meiji in 1869 as a Shinto shrine to commemorate individuals who died in the civil strife that helped restore his authority after centuries of rule by shoguns.
Its role was subsequently expanded. Adherents to Japan's native religion of Shintoism believe the souls of 2.5 million departed ancestors who died in Japan's wars up to and including World War II are enshrined there, with their names and other personal details recorded.
Although it was stripped of its state sponsorship by allied occupiers in 1945, it retains a powerful pull and was visited on eight occasions by wartime emperor Hirohito until 1975.
Q. Many countries have memorials to their war dead, why are China and South Korea annoyed about this one?
A. Japanese nationalists, including Shinzo Abe, like to argue that Yasukuni is no different from the US National Cemetery at Arlington.
But unlike Arlington, Yasukuni peddles a view of history that many find unpalatable. The attached museum portrays Japan more as a victim of US aggression in WWII and makes scant reference to the extreme brutality of invading Imperial troops when they stormed through Asia - especially China and Korea - in the 20th century.
Significantly, 14 World War II leaders - including army general and prime minister Hideki Tojo - who were indicted as "Class-A" war criminals by an international military tribunal, were secretly added to the Yasukuni honour list in 1978. This only became public knowledge the following year.
Q. If it causes so much trouble, why do Japanese leaders insist on going?
A. Not all do. Only 15 premiers since WWII - about half - have paid respects at the shrine and the present emperor has never been (his father stopped going before the 14 senior war criminals were enshrined).
Before Thursday no sitting prime minister had been since Junichiro Koizumi in 2006. Abe stayed away during his first term in office from 2006-2007.
Senior politicians who visit insist they are doing what senior politicians in most other countries do when honouring fallen soldiers.
A smallish but vocal sector of the political right believes Japan is unfairly criticised for its violent wartime past, saying Tokyo's empire-building was no different from European powers.
They believe Japan has more than made amends for the past - they point to huge payments made to Seoul as reparations in the 1960s, and to numerous apologies.
For some of them, a visit to Yasukuni is part of a move to strike a more balanced view of the past, and to demonstrate their nationalist stance.
Q. What's likely to happen now?
A. If past events are any guide, relations between Japan and its neighbours will sink even further.
Abe has met neither Chinese President Xi Jinping nor South Korea's President Park Geun-Hye since they all came to office around the same time 12 months ago.
The United States, which is allied with both South Korea and Japan, finds the squabbling between the two infuriating at a time when it believes the world needs to form a united front against a surging China.
Ties between Beijing and Tokyo were already dire, as they spar over the sovereignty of an island chain in the East China Sea.
Both militaries have been involved, albeit at a distance thus far, but observers warn that a clash - caused by accident or bravado - is increasingly likely, especially as attitudes harden even further with each passing provocation.
They say there could be an increase in activity around the islands.
Disruption to the huge economic relationship cannot be ruled out - the last sudden downward lurch in Sino-Japanese relations, when Tokyo nationalised the islands, was accompanied by major street protests in China that targeted Japanese businesses and badly crimped two-way trade.