This is the 2468th most frequent French word.
vaincu
Defeated.
Here 'vaincue' is used as a future tense passive participle referring to a future event affecting the subject 'Elle'.
Elle sera vaincue lors du prochain tournoi.
She will be defeated in the next tournament.
Here, 'vaincu' is used as a past participle meaning defeated, functioning adjectively to describe someone's state post-defeat.
Il est vaincu après une longue bataille.
He is defeated after a long battle.
The word 'vaincues' is the past participle form agreeing in number and gender with the subject 'forces ennemies', used in a passive construction indicating an event occurrence.