The Civilization series of empire-building games has opened its doors to the Facebook masses, inviting allcomers to try out CivWorld.

In contrast to previous Civ games, in which players would compete against the computer or each other, CivWorld is a more social affair, befitting of a social network.

There is still a core competitive element, but rather than control an entire nation individually, players must team up in order to create nations together and beat other nations by virtue of their accomplishments, be they military, cultural, or otherwise.

Since CivWorld was first announced in 2009, then under the name Civilization Network, serious competitors have sprung up.

Empires & Allies, released June 1, 2011, has accumulated 50 million regular users in just over a month, making it the second most popular Facebook app for publisher Zynga as well as for the social network as a whole.

Age of Empires Online, meanwhile, has its roots in another well-established strategy series, and is preparing itself for a free-to-play launch come mid-August.

CivWorld Facebook page: