The by far most low effort way is to let Aria go do it herself, she'll increase the rebels manpower and power value a little bit daily.Excuse Me, im kinda new to this game can someone tell me how to increase "Power Value" on the "New World Order" Quest For Aria. Thank you.
But the primary way for the player to boost that is donations. The go-to move is to craft swords in a workshop and donate those.
1 stack of a 100 swords = 5 donations of 20 swords = 5 power value.
Additionally if the rebels have some money, but not enough to hire a 100 guys for 300k, occasionally a day-end event will fire where they'll spend a 100k to gain 50 power.
So I tend to keep the rebels at 300k and just keep making swords until the event fires, then go donate them a 100k and all the swords I have.