Pentagon simply cannot ‘under spend’. Hence no peace dividend

The ‘peace dividend’
since fall of Mastodon
seemed a heaven-send
in 1991

But the Pentagon
please try to cotton on
can’t but carry on
needed to bear down on

Despite it’s vainly bloat
it just won’t concede
a single tank, plane, boat
or other war steed

seemed at time providential
turned out inconsequential

+)
-cotton on = understand, or begin to understand
-1991 = the collapse of the Soviet Union (here: Mastodon)