I'm tired, so I will give you the cliffnotes version.
A number of independant kingdoms and player-run cities have always existed on the Baja Shard, but in recent times Lord Casca has seemed their sovereignty and right to rule null and void. He offered these independant realms a chance to argue their case before the High Court of Britannia, but one could argue that it was merely a ruse meant to justify the tyrants actions.
After having proclaimed their sovereignty void, Casca sent armies to the independant states and colonies of the Kingdom of Dawn, the Village of Avalon, the Colony of Horseshoe Island, the Village of Scythe, and the Barony of Darkmor. Our goal, if we choose to side with the Independent Realms, is to fight back and defeat these invaders.
As far as difficulty goes, the monsters are definately on the upper tiers. They aren't invincible, but it basically takes forever for my pure mage to take one down. You either have to have a Sampire, an ABC Archer, or a Greater Dragon to really solo the things. You're better off fighting in a group if you can. I would also be careful, as most of these locales are located within Felucca.