Spoiler warning: this review contains major spoilers for the first season of “Game of Thrones,” and mild spoilers for the season two premiere.

Last year, HBO’s tagline for their ambitious adaptation of George R. R. Martin’s fantasy book “Game of Thrones” was, unforgettably, “Winter Is Coming.” No, it really was unforgettable: in addition to being splashed across every promotional poster and teaser video HBO put out leading up to the show’s debut, we were constantly reminded that “Winter Is Coming,” as the mantra was consistently repeated in every episode.

This season, which premieres this Sunday at 8 p.m., it seems that things have changed in the fantastical realm of Westeros, if only slightly: this season’s tagline is “War Is Coming.” And in the season premiere, it seems as if the encroaching winter and looming war go hand in hand, as the numerous pieces of “Game of Throne’s” bafflingly expansive chessboard move into place to prepare for what promises to be an explosive battle for the throne of Westeros.

For the purposes of this review, it’s futile to try to summarize last year’s season of “Game of Thrones.” Martin’s world is so vast, the alliances and rivalries of the various clans and families so convoluted and the cast of characters so bewilderingly extensive that, rather than trying to catch up through recaps, it’s easier just to go back and watch the first season in one breathless marathon (or, better yet, read the books).

It is, however, somewhat easier to lay out the state of Westeros as it stands at the season premiere. Practically the entirety of the first few episodes of the season are devoted to setting up the cataclysmic rage of a war that promises to end during this round of 10 episodes. King Robert Baratheon (Mark Addy) has died, and though his young teenage son Joffrey (Jack Gleeson) has now inherited his title, the position is precarious and up for grabs by a myriad of competing forces — because word has gotten out that Joffrey Baratheon is illegitimate, a product of incest between his conniving mother Cersei (Lena Heady) and her twin brother, Jaime (Nikolaj Coster-Waldau).

Meanwhile, the repulsively spoiled 13-year-old King Joffrey is doing a predictably horrible job of leading the kingdom, spending his days throwing elaborate parties and tournaments and harassing his court along with his tragic young fiancee Sansa (Sophie Turner), whose father he’s just had executed. The Queen Regent Cersei is the one who’s really been governing the kingdom behind the scenes, but her vicious ruling style is winning her no love from her subjects, who are restless and on the brink of rebellion.

Cersei is in constant struggle with her dwarf brother, Tyrion (Peter Dinklage), for the upper hand in the capitol city of King’s Landing. Some of the most delightful and entertaining scenes of the premiere involve the expertly written and dynamically acted back-and-forth between the siblings, their repartee seething with both malice and wit. (“You love your children. It’s your one redeeming feature. That and your cheekbones,” Tyrion jabs at Cersei).

Showrunners David Benioff and D. B. Weiss’ real challenge, at this point, is to keep their massive canvas from becoming too unmanageably broad. But judging from the tidily rapid pace of the season’s first four episodes, “Game of Throne’s” devoted audience is in good hands.

Printed on Friday, March 30, 2012 as: War comes with second 'Thrones' season