Your argument would be very convenient for socialists or communists looking for an explanation that blames war on the rich. Unfortunately I do believe it is a gross oversimplification that is neither useful nor particularly true.
While it is true that the military industrial complex has gotten out of control in many western countries since World War II, the argument that private industry is the true beneficiary and intentional instigator of war can be readily disproved. Rather, this assumption made by many on the left is born from a partial realization of the truth that war is about resources, but the argument quickly loses the plot thereafter. War is indeed about resources, both physical and psychological in nature, or put more succinctly, war is about security. Each state actor responds and reacts as necessary in order to ensure their legitimate security needs are met.
This view was famously espoused by political scientist Kenneth Waltz when he built upon the theories of classic realists such as Machiavelli. Whereas Classic Realism suggests that war is about power, Waltz takes it one step further with Structural Realism and gives us an academic framework to understand the balance of power and the motivation behind state actors. Waltz suggests that these power shifts are the result of states reacting to perceived threats in order to ensure security. For instance, in the Structural Realist view, one could say that Russia’s invasion of Ukraine is an attempt to gain security in response to a perceived NATO threat. Using this theory, we could similarly suggest that the US invasion of Afghanistan was a move to obtain greater security in a region that threatened the US hegemony (though the argument starts to break down here when we distinguish between the Taliban and Al Qaeda as neo-realism does not explain the action of non-state actors).
While it would be fair to say that in many western countries, the military industrial complex has acquired a massive amount of power and control over the government, it can hardly be said that war exists only for the benefit of war profiteers who help with nation building. The most obvious proof of this is the fact that war long pre-dates crony capitalism, nation building, and the military industrial complex as a whole. Furthermore, while lobbyists do hold an incredible amount of power, they are certainly not the rulers and final decision-makers of our country. Foreign policy is set by a number of diverse lawmakers and civil servants across the political landscape, but the withdrawal of US troops from Vietnam, which was opposed by the Military Industrial Complex, as well as the US intervention in Somalia which was wholly a humanitarian mission, are proof that they do not make the final decisions.
Our democracy certainly has many problems. Money pollutes our campaigns, and lobbyists hold far too much power. Trump’s five year lobbying ban for former US officials was a good start until he repealed it. We need more measures that limit lobbyists, and limit the ability of ANY politician or political party from totally derailing our country by putting us into unnecessary wars. We need more checks and balances in our system that prevent career politicians from fucking the rest of us over. And dammit, we definitely need to elect some better people than these jokers we’ve been electing lately. However; war is far more complex than you suggest.