According to Seven of Nine (in Voy: Relativity), the whole event was a causal loop. Given that the Borg have a pretty reasonable grasp of temporal mechanics, I think we can take her at her word:

DUCANE: [what is] The Pogo Paradox[?]

SEVEN: A causality loop in which interference to prevent an event actually triggers the same event.

DUCANE: Excellent. Can you give me an example?

SEVEN: The Borg once travelled back in time to stop Zefram Cochrane from breaking the warp barrier. They succeeded, but that in turn led the Starship Enterprise to intervene. They assisted Cochrane with the flight the Borg was trying to prevent. Causal loop complete.

DUCANE: So, in a way, the Federation owes its existence to the Borg.

SEVEN: You're welcome. The Seven of Nine paradox.

According to Seven of Nine (in Voy: Relativity), the whole event was a causal loop. Given that the Borg have a pretty reasonable grasp of temporal mechanics, I think we can take her at her word:

DUCANE: [what is] The Pogo Paradox[?]

SEVEN: A causality loop in which interference to prevent an event actually triggers the same event.

DUCANE: Excellent. Can you give me an example?

SEVEN: The Borg once travelled back in time to stop Zefram Cochrane from breaking the warp barrier. They succeeded, but that in turn led the Starship Enterprise to intervene. They assisted Cochrane with the flight the Borg was trying to prevent. Causal loop complete.

DUCANE: So, in a way, the Federation owes its existence to the Borg.

SEVEN: You're welcome. The Seven of Nine paradox.