Boost for a month, America replaced soldiers (7)
I believe the answer is:
augment
'boost' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for augment that I've seen before include "boost" , "Swell" , "Supplement" , "Make greater in size, number, etc." , "Add to, increase" .)