Irrationalism in 'Rings'? So sayeth he...

[The Saucepan Man]

The wars are acts of defence, and play a decisive part in the eventual triumph of Good over Evil.

It is difficult to imagine how, in LotR, war could have been avoided when the "forces of good" were faced by an unremittingly evil power bent on world domination. Rohan, Gondor, Lorien and Esagroth were all attacked by Sauron's forces and had no choice but to defend themselves.

I am interested to know, however, how Tolkien dealt with the reasons/justification for war in his other tales. Since I have not read the Silm (yet), my only other reference point is the Battle of Five Armies in The Hobbit. This starts off as a potential conflict between the Dwarves on the one hand and the Elves of Mirkwood and the Men of Lake-Town on the other. But they team up to defend themselves when attacked by the Goblins and Wargs. So, the battle is forced upon them.

Are there any situations in Tolkien's works where the "good guys" launch an attack on the "bad guys" (other than in self-defence, as with the confrontation before the Black Gate), or where the "good guys" fight a war between themselves (as might have happened at the Lonely Mountain had Bolg's forces not turned up at the right moment)? If so, how are the reasons for such wars/battles dealt with?