According to Wikipedia[1], the biggest U.S. arms companies employ ~700.000 people, so I don't think you need to be a conspiracy theorist when you deduct from this that, if world peace were to settle to the globe it would mean less jobs for the people, less tax income for the government and less profit for the industry. Although most of the sales for these companies come from the U.S. government, according to TIME the export business isn't exactly pocket-change either[2].
[1] https://en.wikipedia.org/wiki/Arms_industry [2] http://time.com/4161613/us-arms-sales-exports-weapons/