The anti-portal countermeasures were a new way of using an existing weapon. The fleets used destabilized antimatter torpedoes to make it impossible for a Portal to open properly nearby. The weapons themselves didn't do much damage, but the effect on portals was nearly perfect, and it would last for days or even weeks.
The hope was that they would be preventing the enemies from appearing among them, which would allow for a better defensive formation.
Then, the waiting started.
The signals were getting stronger by the hour, and the extent of the staging area was unclear, but the extra time was enough to get everyone to break out the big guns, forbidden weapons, and other questionable bits of technology that would never be used under normal circumstances.
If this battle could be won, or even stalled long enough that the enemy could be whittled too low to be able to move on to another solar system with any level of effectiveness.