Finny, in reaction to the fact that he can't get into the war because of his leg, concocts a fictional scenario about how the war wasn't real, but just some fat old men conspiring in a room together, in order to get all of the good food and supplies, getting fatter and richer off of the profits. The rationing that occurs during the war as seen as suspicious, and a way for the rich men to get all the good stuff for themselves and leave the rest of the world without. Finny states,
"There isn't any real food shortage, for instance. The men have all the best steaks delivered to their clubs now."
So, is there any truth to this conclusion about war? In every war, there are certainly people that profit; in fact, people have been made millionaires by wars, either through the legal market, or the black market. Think of tire manufacturers, clothing factories, railways and other resources that wars throughout history have relied heavily upon in order to function. Soldiers need uniforms--clothing companies get rich off of the contracts. They need weapons--artillery companies get rich. On the black market, people who can get their hands on rationed goods make a killing. So, in that sense, there are definitely people profiting from wartime.
As for the deeper root of the conspiracy, that it was just a bunch of political figures that invented the war, if you look at it as them being the ones responsible for declaring and manuevering wars, there is some truth to that. Hitler certainly aimed to create wars and dominate, and manipulated circumstances to have that happen. Often, wars haven't been initiated by the people, but by their leaders in conjuction with the leaders' ambitions. I hardly think that they made the wars up, however. They were real, unfortunately.
I hope that those thoughts helped a bit; good luck!