Imperialism is a one sided relationship, although there are of course inter-imperial rivalries. The US empire is the imperialist, its allies, largely former colonial nations themselves, are really nothing more than vassal states.

The heavy reliance of US allies on the US is by design. These nations didn't have a choice in the matter. That's one of the primary ways the US has survived so long as such a dominant imperial power. Of course these vassal nations participate in adventurism and neo-colonialism in the global south because they have their material interests to attend to, be those nurturing the relationship with the US, enriching their own capitalist class, or staving off revolt in their own populations.