^Depends on how you look at it.
Endgame (the Voyager finale) is what "pissed off" the Borg
The TNG Novel Resistance
is where they first start to appear and cause problems after that.
The TNG Novel Before Dishonor
is where the first really big thing occurs.
The Destiny Trilogy is the whole big event -- and likely is the more direct answer to your actual question.
You left out Greater Than the Sum
, which ties up the loose ends from Before Dishonor
and shows the beginning of the Borg invasion from Destiny
What's potentially misleading here is that the Borg incidents in Resistance, Before Dishonor
, and most of Greater Than the Sum
are actually unconnected to the big invasion that begins in the epilogue of GTTS and continues through Destiny
. To all indications, it's pure coincidence that they happen so close together. But the earlier Borg incidents are important in setting up certain character arcs, particularly Picard's.