Inferno tactics.

I completely agree with QWERTY. It's just silly to engage in a head-on fight against the Barbarians. Inferno has decent magic, and it's essential to use it. For every ancient monster, there's a specific weakness; for every Griffin, there's a slowing spell or Berserk. Or, for example, you can use several Efreet and Armageddon (which is often found in Inferno) to attack someone like Crag Hack. The Barbarian army is slow, so while they overwhelm you with, say, six stacks of one Efreet each, you can manage to cast Armageddon a couple of times (and considering that you can build an Order of Fire in each Inferno, the power of Armageddon can be quite significant) and retreat to get a new batch of Efreet. In general, there are many options. The main thing is that the Barbarian doesn't have a red orb.