Assimilation or annihilation is the declaration of the Borg, which equates to being slavery or death. By that definition the Federation's stand point is that a state of war exists, and will always exist, so long as that is the Borg goal.
Declarations have been made to support that position. Whether the Borg understood them as such, or recognize their own actions as hostile is well... irrelevant.
Both sides understand that the Federation will not willingly comply with Borg demands, and that violent offensive and defensive tactics will be employed against one another, in order to prevent the opposing combatant from achieving their goals. That folks, is war, even if it goes cold once in a while
The problem is that the Federation or at least some in it, are rather unwilling to do what's necessary to win a war like that. Unlike all other wars they have fought, there is only one tactic that can be foremost.
Destroy them, before they can destroy you, unless Guinan's got some brilliant plan to strike up an accord with them, like she postulated might someday be possible, when her & Picard spoke at the end of Q-Who
Otherwise, you do everything you can to destroy as many of them that is necessary to change their goal, and in this case, that may be all of them