Mercenaries are freelance professional soldiers unaffiliated with any particular private military firm or security outfit. They cost nothing to hire, won’t consume your Rations, and can recover a large amount of Resources during raids. The ones you find washed up in the Mercenary Bars in the seedier conflict zones won't take much convincing to join your cause, provided there's free ammo and you don't ask too many questions about their past.
To recruit them, build the Mercenary Bar and Barracks and call in a few favors with friendly Commanders around Zandia.
You can recruit up to three Mercenaries each day by yourself. Ask your Friends and Partners to help you recruit more (up to 50 total) by visiting your Base, going to your Mercenary Bar, and clicking "Recruit Mercenary". You can return the favor by clicking on their Mercenary Bars and helping them recruit more for their operations.
As they’re working strictly off the record, whenever a Mercenary is killed in action, standard policy is to go back to the bar and recruit the next guy in line.
You can also increase your daily Mercenary recruiting limit by purchasing Mercenary Kits. Each Kit permanently adds +1 Mercenary to your daily recruiting limit.