Upfront, never accept the offered alliance (4)

I believe the answer is:

nato

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'alliance' is the definition.
(I know that NATO is a type of global organization)

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for nato that I've seen before include "Military alliance (acronym)" , "Military alliance, formed 1949" , "Atlantic alliance (abbr.)" , "Security agreement" , "Military bloc" .)

I've seen this clue in The Guardian.

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