Ranger "Refugees" - [5th campaign, 1st mission]

I played this mission today. At first, there were a couple of Turquoise attacks on my outposts, but I repelled them. Then, Turquoise attacked one of my outposts and took it over. I ran to recapture it, and Turquoise ran to capture another weakened garrison. I took the outpost back and ran towards the middle of the border where the enemy was heading. A Barbarian attacked the middle outpost, and I was nearby. Before the attack, I moved my army to the outpost and combined it with the garrison's army into one when the demoness attacked. I defeated her without any problems. But I still don't understand the connection between the Barbarian's attacks and the condition of the garrisons.