The military-industrial complex is a really big idea that talks about how the military and businesses work together. Imagine your toy soldiers and your toy tanks were like the real life military.
In the United States, the military has lots of different jobs, like protecting the country and helping other countries when they need it. And businesses make things like weapons, airplanes, and all kinds of other stuff that the military needs to do its job.
Sometimes, businesses want to make money more than they care about helping the military. And sometimes, the military wants to buy things they don't even need just to make the businesses happy.
This can be bad because it can waste a lot of money and make our country less safe. So, people talk about the military-industrial complex to try to make sure everyone is working together to help the country, not just make a profit.