"Merchants of death" is a scary phrase that means companies or people who make money by selling things that can hurt or kill others. It's like if someone sold guns, bombs or tanks. These things are very powerful and can hurt a lot of people if they're not used properly.
Some people believe that these "merchants of death" only care about making money and don't think about the harm that their products can cause. They might even sell their products to people who might use them to hurt others.
Overall, it's important to be careful about what we buy and who we support, so we don't end up supporting these "merchants of death."