“Captain America: Civil War” is what “Batman v Superman” should have been. Thoughtful. Deep. Witty. Fun. It’s a bold political thriller that asks questions about superhero accountability, and it packs a startlingly personal punch.

Captain America/Steve Rogers (Chris Evans) and Iron Man/Tony Stark (Robert Downey, Jr.) clash not because of some misunderstanding that can be resolved by simple conversation (you reading this, Batman?), but because of irreconcilable ideological differences. They aren’t just comic book characters anymore — they’re flesh-and-blood human beings who fight for what they believe.

Both are, in a sense, “right.” Their conflict revolves around the United Nations’ effort to take control of the Avengers. Rogers doesn’t think giving into the UN’s demands is a good idea — nations are governed by agendas, and he thinks the Avengers should not be bent to the will of politicians. Stark sees it differently: the Avengers’ actions have contributed to widespread damage around the world, and they need to be regulated by outside forces before they harm anyone else.

When the mysterious Helmut Zemo (Daniel Bruhl) frames Rogers’ old friend Bucky/the Winter Soldier (Sebastian Stan) for attacking the UN, Rogers goes outside the law to help Bucky take down Zemo — and Stark pursues them.

Chris Evans and Robert Downey Jr. deliver compelling performances that convey the multi-faceted nature of the conflict between their characters, which is driven by the ghosts of their pasts and visions for a better future. They sell the heroes’ antagonism without letting us forget they are supposed to be brothers in arms. For all its joyful moments of superhero brawling, “Civil War” is a tragedy about the dissolution of a friendship. Of the two leading men, Downey Jr. impresses more, offering the best work of his entire Iron Man run.

Another standout is Chadwick Boseman as African superhero Black Panther, who joins Iron Man to avenge his father’s death at the UN attack. It’s thrilling to bask in Panther’s enormous strength as he battles against Captain America and the Winter Soldier. The other scene-stealer is Tom Holland as Spider-Man, who trumps Tobey Maguire and Andrew Garfield with his youthful earnestness and brash wit. While Spider-Man serves little narrative purpose other than to quip and dazzle during the film’s destined-to-be-iconic airport showdown, he lights up the picture with his presence.

“Civil War” is brimming with many more characters, such as Scarlet Witch (Elizabeth Olsen), Vision (Paul Bettany), Ant-Man (Paul Rudd) and Black Widow (Scarlett Johannsson). But in spite of its large cast, this Marvel entry is very focused. The Russo brothers prove a fine pair of directors, developing almost every character on the roster without ever making the narrative feel over encumbered. We learn about the heroes’ motivations and what makes them choose the side they’re on. Even Zemo is sympathetic — it’s hard to call him a villain when you learn why he’s out to destroy the Avengers.

The Russos wisely tie every character’s arc into “Civil War’s” questions about accountability. The film heavily explores the debate between Rogers and Stark, but doesn’t end with any definitive conclusion as to whose beliefs are better. The Russos develop the movie’s ideas so they address real-world problems, such as the War on Terror and American foreign policy. It asks us to consider the cost of violence and to think about what heroism truly is.

“Civil War” spends so much time building up its human element that its spectacle becomes all the more involving. There are many sequences of intense, cleverly-staged action filled with money shots, memorable dialogue and wonderful character moments. Don’t let anyone spoil how they play out for you — the surprises are worth the wait.

The Marvel Universe has given us alien warlords, megalomaniacal robots and apocalyptic threats, but the smaller-scale “Civil War” has told the most engaging tale of the series. The Russos understand that it’s not the size of the story’s conflict that matters, it’s how much that conflict matters to its characters.

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• “Captain America: Civil War”
• Running Time: 147 minutes
• Rating: PG-13
• Score: 5/5 stars