I found that when I was a warrior and I was up to the last cave, I was around lever 33/34, and and needed to be allied to the Alliance to get the last cave quest. I went back to see if there was any quests that I'd missed out on, and when I went back, I fought some level 4's or something, and they were doing -ve damage. So I got all of them attacking me and walked away for a bit and came back and my hp was about 70k, and then I went and did the last quests and it was easy :) so if that helps you, yeah.. That's just what I found I don't know if anyone else noticed it.
I really like this game. I mean I must admit I get a bit annoyed when they shell you and every shell seems to fall in your trench, and then you do the same to them and none of their guys die. But then there is times where the opposite happens. I love it when you can just get a whole lot of assault troops and just storm the other side.. And then they're like rahh dakka dakka dakka boom boom and yeah I'll shh now.
5/5 from me :)
 "Hands of War"){kind=icon}
 "Bloons Tower Defense 3"){kind=icon}
 "Warfare: 1917"){kind=icon}
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 "Pillage the Village"){kind=icon}