Worlds from this game:

  • (1 million unnamed, just mentioned by number in the opening)
  • 2 named
  • several unnamed with missions in-game upon them

 

The homeworlds of the opposing sides:

  1. Core Prime:  home of The Core; the empire based in the middle of the Milky Way
  2. Empyrrean:  home of The Arm; the empire based in the spiral-arms of the Milky Way

 

Missions/Worlds of the Arm:
(These are the titles of Arm (anti-Core) missions in the game, not of the worlds those missions were on.)

A Hero Returns
Core KBot Base, Destroy It!
Spider Technology
Core Contamination Spreads
The Gate to Thalassean
Beachhead on Thalassean
The Defense of Larab Harbor
The Gate to Tergiverse IV
The Hydration Plant
The Bromid Maze
The Gate to Barathrum
Barathrum!
Landown’s Interface
The Heat Increases
Rougpelt
Stockpile at the Abutment
Fortress at Brooban’s Isle
Vengeance!
The Motien Ramp
Dump
Welcome to Core Prime
Battle for Coordinate 6551:447
Crossing Aqueous Body 397
Breakthrough to Central Consciousness
Core Prime Apocalypse

 

Missions/Worlds of the Core:
(These are the titles of Core (anti-Arm) missions in the game, not of the worlds those missions were on.)

The Commander Reactivated
Vermin
Ambush!
Enough is Enough
Barathrum!
The Cleansing Begins…
Pulling the Noose Tight
The Gate to Aqueous Minor
The Purgation of Aqueous Minor
The Gauntlet
Isle Parche
A Traitor Leads the Way
Rougpelt
Scouring Rougpelt
Xantippe’s Abyss
Departing Rougpelt
The Lost Isle
Slolam Pilago
The Vebreen Fleet
The Gate to Aegus
Aegus…Empyrrean’s Guardian
A Big Empyrrean Welcome
The Fortress Falls
Surrounded and Pounded
Empyrrean’s Final Stand

 

Details here and here.

1,000,000 worlds in a cube formation is only 100x100x100.
If 10 worlds per system, it is ~46x46x46;
even though 1,000,000 worlds were affected, they might still have been in a very small area of the Milky Way galaxy, and at least affected <1% of the worlds in this galaxy.