What does Eisenhower mean by a "military-industrial complex" and why does he
warn against it?

Explanation:

If you join the needs of the military (weapons like planes and battle ships and flame throwers and rifles and tanks and jeeps) with industry which can provide all those things, you endanger freedom and democracy.

I say that because there is not longer any competition. The military pays for what it needs with tax-payer dollars, and the big companies in industry just get bigger and bigger.

Why is this dangerous? It is because industry can dictate terms to government. "Do as we say or our factories in your state will evaporate and then what do think voters will do? You will lose them their jobs. And don't think we can't do it. We can."

the answer is states.