What led Shinzo Abe to resign?

By Chris Hogg
BBC News

The news of Abe's resignation came as a surprise to many Japanese

Japan's Prime Minister Shinzo Abe has caused a political earthquake, rocking the establishment with his surprise announcement that he was stepping down.

The resignation news conference was a spectacle.

Japan's normally more deferent press corps demanded angrily and repeatedly: "Why?"

They got little satisfaction from the answers he gave them.

So what is the real reason he has decided to go?

It is possible that a deal was done between grandees in his party, the Liberal Democrats (LDP), and their opposite numbers in the opposition.

Japan's government needs to get parliament to give permission for the country's self-defence forces to continue to provide logistical support to the US military in Afghanistan - a plan which has been opposed vigorously by the opposition.

Some suspect Mr Abe's scalp may have been offered in return for opposition support for the controversial new law.

The United States has put a lot of pressure on the government to get the anti-terrorism legislation passed so that the supply operation for its troops can continue.

Mr Abe's colleagues may have realised he had become an obstacle to getting that achieved, and therefore needed to be removed.

Ill health?

But that is not the only possible reason that has been given for Mr Abe's decision.

Shinzo Abe has been in office for less than a year

Some analysts talk about concerns over his health - and rumours that he has been under great "strain" were confirmed by the chief cabinet spokesman, although he refused to give any further details.

But Mr Abe has just returned from a three-nation summer tour, and only last weekend showed no signs of illness during the Apec regional summit in Australia.

The suddenness of the announcement has of course led to speculation that there is something more sinister behind it, perhaps a further scandal that is yet to become public.

As for that, we will just have to wait and see.

It is possible that he has just, at last, come to realise what others have known for some days now - that he had been so weakened by the defeat in this summer's elections for the upper house of parliament that he was prime minister in name only and had no power to get anything done.

The loss of the upper house for the first time in his party's history did not just mean the opposition could block the continued deployment on the self-defence forces in support of the Americans.

It also meant that they could disrupt his whole legislative programme, should they have chosen to.

Weak link?

And as this first parliamentary skirmish got under way, perhaps Mr Abe, or more importantly those around him, realised that with him at the helm the ship would flounder.

The LDP will now be turning its attention to who the next leader is

Of course there will be those who say this is just business as usual. Japanese prime ministers do not usually last long.

Mr Abe's predecessor Junichiro Koizumi was unusual because he lasted five years. Mr Koizumi's predecessor, however, had lasted, like Mr Abe, just a year.

So we are back to the revolving doors of men in grey suits.

Mr Abe will be remembered for the success he had in rebuilding relations with China and South Korea.

But he will probably not be remembered for long.

In the meantime, as with any earthquake, there are likely to be aftershocks in the coming days, as Japan's governing party tries to work out what it should do next.