How difficult is this game?

[VedalkenBear]

AFAIK, the AI picks on players and territories that it sees as weak. For the player aspect, this is generally comparing the Army Size graph scores. For the territory aspect, this is generally a place with no troops and little/no PD. So, as should be pretty commonsensical, having a large army, and having it at your borders with an enemy, should deter that opponent from attacking you.