Three warring space civilizations vie for control of the stars in the utterly engrossing strategy game "Sins of a Solar Empire."

Each faction has a background story, but the game lacks any narrative beyond the framing of this interstellar conflict. There is no single-player campaign, just a large set of stellar maps tailored to a variety of strategic situations for anywhere from two to 10 players.

Of course, "Civilization IV" and other turn-based strategy games eschew narrative-driven campaigns. But the setup for "Sins" is interesting enough that one hopes its makers will see fit to create a story-driven expansion someday.

The factions are the Trader Emergency Coalition (regular humans), the Advent (cybernetically and psychically advanced humans) and the Vasari (vestiges of an alien empire). Each side has a similar selection of structures, frigates, cruisers and capital ships, though their capabilities are not identical.

The game installs key elements of turn-based "4X" strategy games — explore, expand, exploit and exterminate — into a real-time framework. Players are beholden to the raw time it takes to develop planets, create fleets and move those fleets between worlds.

Each side has two large technology trees, one for military and one for civilian research. These are further segmented into three sub-trees: Weaponry and defense will be in one segment, colonization and refinement in another. The game gets confusing here, as different factions don't always have similar upgrades in comparable sub-trees.

At the end of each tech tree lies a devastating superweapon — the TEC builds an enormous planetary siege cannon, the Vasari uses a weapon that can damage or disable everything in a planet's gravity well, and the Advent employ what's best described as a culture gun that can inspire enemy worlds to revolt.

And then there's the online play, where alliances are more unpredictable — largely thanks to the presence of a powerful (though optional) pirate faction. These guys attack the player with the highest bounty, a sum that can be anonymously raised by any player against any other player.

The length of a typical game highlights one of the few flaws in "Sins": The artificial intelligence cannot surrender. This is an oversight that should be corrected.