How does galactic war determine difficulty?

Was supposed to be a comment, but grew too large:

Don t have any other source than my own experience, but it seems to be linked to your Arena rank.

The game inform you the team you are facing are real player team, so it would be logical to take player rank into account for difficulty.

Furthermore, I usually do Arena battle after completing Galactic War, and always end them. The only time the enemy was too powerful for me was when I ranked up in arena before facing GW.

TL:DR: without any source nor enought hard data, I would say from personal experience it is linked to your Arena Rank.

As of the latest version update (22/11/2017), GW is now capped at the difficulty a new player who has just reached level 85 would receive.

Once you're level 85, regardless of how powerful your own squads become, GW will have the same difficulty.

Everyone who has responded is incorrect. I win using 2 characters, and even though my GP is quite high and my best two squads are over 100,000, my final battles are up against squads that I can beat without even looking at the screen. Here is how:

Whittle down the GP by using your best squad to kill off a few. Lose on purpose in the final battle to win with a weaker squad. Over time, the GP of all battles will lower. I have won a few hundred on auto and set my last squad at something lower each time.

After I add another Zeta to my Revan or Darth Revan, I will solo the final battle with them. Then I'll start using something like Yoda+Anakin, etc., to keep lowering the Galactic War difficulty.