Armed clash between South Korea/Japan feared over disputed islands

[WMS]

If a war does break out, this will be a prime example of two democracies going to war with each other.

It will be the only example

There's a few more. I think both India and Pakistan were democracies when they fought their first war. There was a big Peru/Ecuador border conflict for awhile, and after the breakup of the Soviet Union there was a bunch of cases of Russia giving lots of military aid to seperatists campaigns in some other former Soviet republics, most of which were more or less democratic (at the time at least). Another case where this almost happened was Greece/Turkey.

and neither country is truly democratic. They are what I call  'semocracies'. Democratically elected government with no real opposition.

True of Japan, but not South Korea.

I would suggest looking at the arguments here

[WMS]

That doesn't mention the El Salvador/Honduras war that started over a soccer game. I think both contries were democracies at the time.

Well...that's rather doubtful for El Salvador (not at all a freely and fairly elected government), and a bit less doubtful for Honduras.

[WMS]

From what I understand, prior to the 80s El Salvador had a more or less democratic although often authoritarian government. Note it had a 2,3 Freedom House rating until then.

Hmm...prior to the 80s Freedom House had some damn odd ratings...ironically enough the coup (either 1979 or 1980 - I would check Wikipedia but the site appears to have gone bonkers with the font or something) actually was designed to improve matters - it was a centrist coup against a rightist regime, if you can believe that...