The enotes section entitled Themes goes into some of these in great detail, you can find that here: http://www.enotes.com/war-worlds/46163
But briefly, thinking about Man versus machine, for example, I think the novel is pretty clear that it would have to be living creature and Machine that destroys the world, the machines couldn't do it themselves. Think about the martians themselves, they get the power when they climb into the machine, before that they are small and weak, and not that threatening, but consider them together and they could destroy humanity. Look at this passage of the book from Chapter 10 of book 1: . . it was no mere insensate machine driving on its way. Machine it was, with a ringing metallic pace, and long, flexible, glittering tentacles (one of which gripped a young pine tree) swinging and rattling about its strange body. It picked its road as it went striding along, and the brazen hood that surmounted it moved to and fro with the inevitable suggestion of a head looking about.
That's a passage from when a martian is inside a machine, suddenly, its working and its dangerous, and the martian is as well. Therefore the machine needs a living creature, it cannot do it on its own.