MMORPG.com Final Fantasy XI Correspondent Malcom Calivar writes this overview of the conquest system in Square Enix's contribution tot he MMO universe.

Vana'diel is a land torn by conflict. Concealed within its enchanting forests, arid deserts, and lush tropical jungles lies a threat too powerful for any one nation to combat alone. The Crystal War has ended, but the beastmen still wander the many regions of Vana'diel, posing a threat to travelers. The three main nations of Vana'diel seek to secure these regions, not just from wandering beastmen, but from each other, as well. Although technically allies, it is no secret that these nations seek to expand their own borders to grow in power and wealth. However, involving their respective armies in such a conflict could lead to a full blown-out war between these nations. Luckily, the nations have found a way to expand their borders and make it seem as nothing more than civil competition between their citizens. This is where you come in. Seeking to secure these regions without involving their own military forces, the three main nations of Vana'diel have enlisted the aid of adventurers to keep the beastmen population in check, and help them achieve ultimate conquest.

Read the Conquest System Overview