Japan's government has recently begun implementing its reinterpretation of the Peace Constitution. For more than 60 years, Japan has foregone the right to use military force except in self-defence, but the new changes being implemented by the ruling Liberal Democratic Party (LDP) mean Japan will now exercise the right to "collective defence".
Here, collective defence means providing military force in defence of an ally. What does this mean in real terms, though? I think its fair to say that if a nation allied to Japan came under attack, that the Japanese government would be quick to forget the peace constitution and make ready to commit troops anyway, where such a conflict was endangering Japanese security. One example often touted by the media is the new ability for Japan to shoot down missiles from (for example) N. Korea, that were headed for an allied country (i.e. the USA). I would conjecture that even without the reinterpretation of the constitution that Japan would do this, because it cant risk losing face to America because of its dependence on the US for trade, and it could easily justify the action after the fact. The same goes for any conflict involving major trading partners.
In this light, the reinterpretation seems very much like what Japan has been continually doing: posturing. There is overwhelming support among the political parties of Japan for the reinterpretation, and so we can probably assume that (for example) shooting down a couple of North Korean missiles would be received relatively positively over here, regardless of the constitution. The real power of the changes is political: PM Shinzo Abe will gain a fair amount of domestic support from this move.
The problem with such reinterpretation of the constitution is the same problem with Japan that it has always had from posturing: international relations. China and S. Korea have both objected to the change, and the reinterpretation of the peace constitution provides a tempting foundation upon which to criticise Japan. It would be easy at this point to paint Japan as re-militarising, increasingly extremist, and unwilling to resolve disputes diplomatically.
It makes me wonder, is the gain in domestic support really worth the loss of respect in Asia? Then again, does this political posturing really have any impact on trade?
EDIT: Reading the paper this morning, while Abe managed to push this through through the government, it isn't riding well at all with the public: Polls suggest public support for the Abe cabinet has dropped under 50%, with 54.4% disagreeing with the move, and only 34.6% agreeing. Its kind of nice to know the Peace Constitution is valued by the Japanese people, and this raises some questions over the validity of Abe's actions; however, I'd like to think that the Japanese people don't in principal object to the idea of shooting down missiles en-route to their allies..