From Boardgame Geek:
This entirely new shiny edition of Tomorrow's War is now
a game on its own, and is no more considered an
expansion of the Force on Force basic rules. It is also the
first one to be actually printed,
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A previous sort of "beta" edition was just sold as a .pdf
and as an expansion for the Force on Force basic game.
Extended play testing and feedback has permitted the
developing of a stand-alone game.
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From the Introduction in the book:
Tomorrow’s War is a science fiction military miniature
war game with emphasis on "hard" science fiction rather
than "Space Opera" or "Science Fantasy." This rule book
contains background material for gaming in
Ambush Alley's campaign setting, but the rules
themselves are not background dependent. You can use
them to game gritty science fiction engagements against
whatever narrative backdrop you choose.
Tomorrow’s War can be played with figures of any scale.