Final answer:
Iron triangles contribute to high levels of military spending due to the symbiotic relationships between Congressional committees, executive agencies, and interest groups that lobby for defense funding.
Step-by-step explanation:
The phenomenon of iron triangles is an aspect of American politics where there is a symbiotic relationship among Congressional committees, executive agencies, and interest groups, which often results in increased military spending in the United States. Option 3 is the most accurate explanation for how iron triangles contribute to high levels of military spending. These triangles generally lead to a convergence of influence and interest among these parties, with interest groups heavily lobbying Congress and bureaucratic agencies, which in turn helps to secure funding and policy favorable for them, including in the realm of defense. This arrangement can also distribute spending across congressional districts, incentivizing Congress members to support defense spending. The military-industrial complex that President Eisenhower warned about highlights such relationships, where defense contractors seek to exert influence on government leaders to increase military budgets.