How do I beat Barbarians on the map?

You find barbarians on the map by tapping the magnifying glass on the bottom left of the screen. Then tap the barbarians icon and drag the search bar to the level you want to fight.

You can usually only increase it to one more than the max level of Barbarians you have already defeated.

For higher level barbarians it is a good idea to send in two or three sets of troops to defeat them, especially if you cannot do it with just one commander group.

Another benefit of sending multiple commanders to the same barbarians is that if there is a victory you get the same prize more rewards / eg twice as much for two armies, and three times as much for three sets of armies.