Could this be "Twilight of the Gods" by John C. Wright? This was published in 2009 in a collection called "Federations" edited by John Joseph Adams. I have not read it myself, but according to an interview with the author:

The story springs from two roots. First, this is my attempt to tell the story of Wagner’s Ring of the Nibelungs in space, complete with elfs and dwarfs and mortals and immortals. Second, this is a sequel to my first two short stories sold, NOT BORN A MAN and FARTHEST MAN FROM EARTH

which fits with the Wagnerian theme you describe. A synopsis is given as:

TWILIGHT OF THE GODS is a tale of a multigeneration warship that continues in the interstellar fleet action in which she is involved, long after the mortal officers, crewmen and marines have forgotten the meaning of the titanic eon-long battle around them. Due to an invasion of the lower decks by enemies, and the mutiny among the officers, control of the long-quiescent battlecomputers is lodged in a single set of codes carried on a ring—as far as the crew is concerned, this is a magic ring, and whoever possesses it becomes the captain of the steel universe around them. Conflict erupts when a lone wanderer from the heavy outer decks of the world-ship appears, bearing the fatal ring, and seemingly loyal to the ancient, long-lost sailing orders of the forgotten generations who launched the mighty warship. For he believes, although he has never seen them, that there are other warships beyond the steel walls of the world, friend and foe alike.

which fits with the theme of a generation ship having an internal civil war.

It has also been published in "The Year's Best Science Fiction: 27th Annual Collection", edited by Gardner Dozois, so it seems a good candidate for the story you remember.

Could this be "Twilight of the Gods" by John C. Wright? This was published in 2009 in a collection called "Federations" edited by John Joseph Adams. I have not read it myself, but according to an interview with the author:

The story springs from two roots. First, this is my attempt to tell the story of Wagner’s Ring of the Nibelungs in space, complete with elfs and dwarfs and mortals and immortals. Second, this is a sequel to my first two short stories sold, NOT BORN A MAN and FARTHEST MAN FROM EARTH

which fits with the Wagnerian theme you describe. A synopsis is given as:

TWILIGHT OF THE GODS is a tale of a multigeneration warship that continues in the interstellar fleet action in which she is involved, long after the mortal officers, crewmen and marines have forgotten the meaning of the titanic eon-long battle around them. Due to an invasion of the lower decks by enemies, and the mutiny among the officers, control of the long-quiescent battlecomputers is lodged in a single set of codes carried on a ring—as far as the crew is concerned, this is a magic ring, and whoever possesses it becomes the captain of the steel universe around them. Conflict erupts when a lone wanderer from the heavy outer decks of the world-ship appears, bearing the fatal ring, and seemingly loyal to the ancient, long-lost sailing orders of the forgotten generations who launched the mighty warship. For he believes, although he has never seen them, that there are other warships beyond the steel walls of the world, friend and foe alike.

which fits with the theme of a generation ship having an internal civil war.

It has also been published in "The Year's Best Science Fiction: 27th Annual Collection", edited by Gardner Dozois, so it seems a good candidate for the story you remember.

Could this be "Twilight of the Gods" by John C. Wright? This was published in 2009 in a collection called "Federations" edited by John Joseph Adams. I have not read it myself, but according to an interview with the author:

The story springs from two roots. First, this is my attempt to tell the story of Wagner’s Ring of the Nibelungs in space, complete with elfs and dwarfs and mortals and immortals. Second, this is a sequel to my first two short stories sold, NOT BORN A MAN and FARTHEST MAN FROM EARTH

which fits with the Wagnerian theme you describe. A synopsis is given as:

TWILIGHT OF THE GODS is a tale of a multigeneration warship that continues in the interstellar fleet action in which she is involved, long after the mortal officers, crewmen and marines have forgotten the meaning of the titanic eon-long battle around them. Due to an invasion of the lower decks by enemies, and the mutiny among the officers, control of the long-quiescent battlecomputers is lodged in a single set of codes carried on a ring—as far as the crew is concerned, this is a magic ring, and whoever possesses it becomes the captain of the steel universe around them. Conflict erupts when a lone wanderer from the heavy outer decks of the world-ship appears, bearing the fatal ring, and seemingly loyal to the ancient, long-lost sailing orders of the forgotten generations who launched the mighty warship. For he believes, although he has never seen them, that there are other warships beyond the steel walls of the world, friend and foe alike.

which fits with the generation ship having an internal civil war.

Could this be "Twilight of the Gods" by John C. Wright? This was published in 2009 in a collection called "Federations" edited by John Joseph Adams. I have not read it myself, but according to an interview with the author:

The story springs from two roots. First, this is my attempt to tell the story of Wagner’s Ring of the Nibelungs in space, complete with elfs and dwarfs and mortals and immortals. Second, this is a sequel to my first two short stories sold, NOT BORN A MAN and FARTHEST MAN FROM EARTH

which fits with the Wagnerian theme you describe. A synopsis is given as:

TWILIGHT OF THE GODS is a tale of a multigeneration warship that continues in the interstellar fleet action in which she is involved, long after the mortal officers, crewmen and marines have forgotten the meaning of the titanic eon-long battle around them. Due to an invasion of the lower decks by enemies, and the mutiny among the officers, control of the long-quiescent battlecomputers is lodged in a single set of codes carried on a ring—as far as the crew is concerned, this is a magic ring, and whoever possesses it becomes the captain of the steel universe around them. Conflict erupts when a lone wanderer from the heavy outer decks of the world-ship appears, bearing the fatal ring, and seemingly loyal to the ancient, long-lost sailing orders of the forgotten generations who launched the mighty warship. For he believes, although he has never seen them, that there are other warships beyond the steel walls of the world, friend and foe alike.

which fits with the theme of a generation ship having an internal civil war.

It has also been published in "The Year's Best Science Fiction: 27th Annual Collection", edited by Gardner Dozois, so it seems a good candidate for the story you remember.