I don't disagree, but I think you're neglecting to consider that there is a relationship between defense contractors making money and politicians making war. Not per say causal, a more complex one than that, but incentives can align and push things into happening even in the absence of explicit quid pro quo. Eg, defense contractors can spread projects out over many states to maximize the political impact of their economic activity; politicians observe that war brings money into their state; their incentives have become more aligned, but no laws were broken or bribes exchanged.

There are many ways for this to happen, and all of them occur (to some degree) simultaneously and the impact is cumulative.

The result is that you cannot create a lasting solution by addressing one side of the equation or the other. You have to address them both, simultaneously, or the system will form again for exactly the reasons if formed before.