15 down
Effusion
from
armies
regularly
upset
people
(9)
Effusion from armies regularly upset people (9)
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The definition is at the beginning of the clue.
How the clue works
Look at Effusion — that's your definition. Pull out the alternate letters (the odd ones) from armies and you get A, M, E, which is then upset (reversed) to give EMA. Tack on people, meaning NATION, and the whole thing comes together as EMANATION.