Is an Action card resolved before or after an initiated clash?
IMHO, the action card is resolved when the clash ends.

This is not made explicit in the rules, but on p. 7 of the rule book it says (under "Play a Season Card"): "The player plays the card, resolves the indicated effect, and then discards that card." This would mean that everything triggered by the Action Card (such as a clash) is resolved before it is discarded, and thus, by association, that an Action Card is only fully resolved after all its effects have been resolved.