And through the barricades..."
Alice and Bob are in love with each other. However, they belong (or are considered to belong) to different factions that are locked in some kind of war with each other. This may be nations or civilizations in a regular war, the factions of a civil war, Feuding Families, or whatever.
The lovers are likely to not be Star-Crossed Lovers: In some works they are, but in others they are never kept apart. Instead, the drama is about how they have to fight for their love or what a high price they have to pay for it as people shun at least one of them as being Category Traitor. Or simply the internal struggle of hating one lantion/faction/family/whatever while loving one member of it. Don't be surprised if some Straw Loser antagonists goes all Entitled to Have You.
Compare Ethical Slut. If Love Across Battlelines is combined with Troubled Sympathetic Bigot, also compare Sex Is Evil and I Am Horny as well as Love Redeems. If the lover is an antagonist rather than a citizen/relative/whatever of the enemy nation/family/whatever, see instead Dating Catwoman if she remain a villain and Defecting for Love if she makes a Heel–Face Turn / High-Heel–Face Turn. Note that a Love Across Battlelines plot often doesn't have this division into a good side and a villainous side - it is common that Both Sides Have a Point and that the protagonists view the conflict as a senseless Good Versus Good.
- A staple in the various Gundam series, as part of its traditional Love Hurts aesop.
- In K, Scepter 4 and HOMRA are more or less enemies... but the top 3 of both sides have constant Ship Tease that's more than just Foe Yay. Luckily, in season 2, they make an alliance with both of them and the Silver Clan, but look at the opening fight scene of the second season. While Saruhiko and Misaki aren't exactly on speaking terms at the time of the series, Mikoto and Reisi's interactions and Izumo and Seri's interactions make it clear they'd rather be doing things other than fighting. And Izumo clearly knows Misaki and Saruhiko won't stay enemies forever.
- Histrionix and Melodrama in Astérix and the Great Divide, where the battle lines are literally a trench cut through the town.
- An Angel and a Demon in Preacher. At one point, the Angel is laying out the whole story in truly florid Purple Prose and Jesse interrupts: "What is this, your letter to Penthouse? You fucked her. She got pregnant. They caught you. I know this part." It turns out they weren't actually in love - they were forced into it by God Almighty specifically to create Genesis.
- Alana and Marko in Saga whose respective homes, the planet Landfall and its moon, Wreath are wrapped up in a prolonged and bloody war.
- In the Discworld of A.A. Pessimal, the love story is the mixed-race romance of Julian Smith-Rhodes and Ruth N'Kweze. Julian isn't just a white guy. He isn't quite the heir - but in the line of succession - to one of the richest and most influential men in Rimwards Howondaland. She is a Princess in the Disc's analogue of Black Africa. Julian's country is stuck in The Apartheid Era and what he's up to with Ruth is not only socially shocking, it's illegal. Ruth's nation is in a perpetual Cold War with Rimwards Howondaland, one which occassionally gets hot. At least partly because of apartheid. As all this is happening in faraway Ankh-Morpork, people around them collude to keep their secret, and their families accept it as one of those things. The rules are different in the Big City. But sooner or later both need to return to their respective homelands.
- In Avatar, the protagonist is a human soldier falling in love with a warrior of the tribe he's hired to defend the evil megacorporation against.
- Oboro and Gennosuke of Shinobi are Starcrossed Lovers from Feuding Families who are in the chosen 5 from each side to fight to the death.
- Sonja and Lucian in Underworld: Rise of the Lycans. The never-ending feud between vampires and werewolves becomes a full-out war because of their relationship.
- In Sterne, between "Walter", a conscience-stricken German corporal, and Ruth, a Greek Jew imprisoned in the nearby concentration camp.
- Kat and Marco in The Shadow of the Lion. Their subplot includes several Shout Outs to Romeo and Juliet.
- Aral and Cordelia when they meet for the first time in Shards of Honor.
- Gawyn and Egwene end up on opposite sides in the schism in the White Tower in The Wheel of Time.
- Susanna and Marc in 1634: The Bavarian Crisis. Susanna was Catholic, and Marc a Calvinist, which was a pretty big deal during the 17th century, particularly during the Thirty Years' War.
- Torquato Tasso's Gerusalemme Liberata features a sub-plot involving a heathen amazon Clorinda and a christian knight Tancredi in love but on opposite sides. Eventually, they end up fighting each other (she was disguised in a full armor) and the girl is mortally wounded by Tancredi and dies.
- Tomorrow War series by Alexander Zorich began with neo-Zoroastrian colonists as a potential enemy whom Terran military with first-hand knowledge admire and envy for neat, honorable and determined traits even while abhorring dystopian sides of their society. The protagonist Space Cadet volunteered into joint operation against an alien threat, its participants were received with great hospitality and praised. He ended up in a Love Triangle with two lady officers, then betrothed to one, then the war began and he met both, but not before realizing that with his bride and a good friend somewhere there it doesn't feel the same as blowing up unknown Worthy Opponents.
- Succession has Rana and the Rix commando, as well Laurent and Nara who are on completely opposite sides of political spectrum and have tremendously differing views on the Emperor however Laurent comes to agree with Nara.
- Warrior Cats has this happen several times. Inter-Clan romances are banned specifically because they lead to the conflict of loyalty to Clan vs. loyalty to mate in a battle, but this doesn't stop these relationships from forming.
- In Fall of Giants, there are Walter von Ulrich and Lady Maud Fitzherbert, who are from Germany and Great Britain respectively. Since they are both of noble birth, their families would have no problem with their relationship - if it weren't for the fact that they happened to fall in love shortly before World War I.
- In Black Dagger Brotherhood, The Chosen Layla and the Leader of the Band of Bastards Xcor are in love and in opposing sides of a civil war. Layla is loyal to the legal monarchy and is expecting the child of one of the King Wrath's Elite warriors. Xcor is trying to overthrow the king. But for Layla's sake he is trying to find bloodless methods via loopholes and caveats in the old laws.
- Played for Drama in The Nightingale (Kristin Hannah) between Vianne and Captain Beck. Although both of the characters simply miss intimacy more than they actually care for each other, their relationship eventually becomes rife with UST (complete with Held Gazes and an Almost Kiss). The subplot is finally resolved when Vianne is forced to cave his head in with a shovel when he discovers her sister concealing an Allied airman.
- In the Bulgarian short story The Peach Thief, the wife of a Bulgarian colonel falls in love with a Serbian POW. He gets shot for breaking into the colonel's mansion to steal the eponymous peaches.
- This is one of the main themes of North and South (Trilogy). Pretty much everyone experience this kind of heartache as the nation is torn apart. The main storyline is of the love between the northern family Hazard and the southern family Main.
- The main protagonists George Hazard and Orry Main are Heterosexual Life-Partners, forced to fight on opposing sides in the war.
- George has a little brother and Orry has a little sister (Brett, not the other one) who are engaged to each other.
- Orry's Love Interest Madelaine is trapped in an Arranged Marriage with an evil southerner who is in another political camp in the South's internal power struggle.
- George's wife is Catholic, making some of George's relatives consider her an enemy in the religious war between Protestantism and Catholicism.
- Finally we have Virgilia, taking the "wrong" side in the ongoing "race war", falling in love with a black man.
- In White Collar Mozzie imagines that his mother and father were respectively Russian and American spies.
- In the WWII miniseries Island at War a British Channel Islander and a German airman fall secretly in love for little other reason than to evoke this trope. To make matters angstier, he might have dropped the bomb that killed her father.
- In Cold War rock opera Chess, Florence, a Hungarian refugee whose father was captured and possibly killed by Soviet troops during the Budapest Revolution, falls in love with the Russian grandmaster who is representing the USSR in a International Showdown by Proxy chess match.
- Romeo and Juliet is probably the Trope Codifier. Romeo and Juliet, children of the violently feuding Montague and Capulet families, fall in Love at First Sight when Romeo crashes a Capulet party.
- West Side Story is Romeo and Juliet in New York with rival street gangs. Tony and Maria fall in Love at First Sight at a dance which the Jets and the Sharks hold on "neutral territory."
- Aida: The titular character and her lover Radames.
- The Light Princess: Althea, the eponymous Light Princess, and heir of her kingdom, and Digby, The Solemn Prince, heir of the rival kingdom. Bonus points for falling in love in the no-man's land between the two kingdoms immediately following a battle.
- In Rossini's opera of William Tell, during the Austrian oppression of the Swiss, Arnold Melchthal, son of a Swiss elder, loves and is loved by the Hapsburg princess Mathilde, and torn between his love for her and for his country.
- In the Mitsumete Knight franchise, this is one of the possible pairings, between the main male protagonist and Raizze Haimer:
- In the Dating Sim game, he's a Dolphan mercenary, she's one of the Eight Generals of Valpha-Valaharian, who will be, especially at the end of the game where she'll want to avenge her fallen leader and father by the hands of the protagonist, be torn between her duty and her love;
- In the RPG game, he's the Captain of Orcadia's Royal Knights, she's a Noble Fugitive from a aristocrat family of the fallen Parmet Kingdom; she'll try to assasinate him several times before gradually growing fond of him, and later, if you're following the Licence of Heartless Odd Number route, he reveals to her he's the Crown Prince of Parmet in hiding, and just as much out for revenge against Orcadia as her: after this, they'll completely fall in love with each other..
- Oichi and Nagamasa in some scenarios of Samurai Warriors, since Oichi's the younger sister of Oda Nobunaga.
- In Tales of the Abyss, you can spend a long Match Maker Quest getting General Aslan Frings of Malkuth together with General Jozette Cecille of Kimlasca, although they won't get properly engaged until after you stop the war. Too bad Frings gets killed by the plot soon afterward, whether you did the sidequest or not.
- Kieri the angel and Buwaro the demon in Slightly Damned.
- Aldran's parents in Anti-Heroes, also an celestial and a fiend.
- For a time in The Order of the Stick, Therkla the female orc ninja was in love with the bard Elan. He was at the time a close ally of the paladin-king Lord Hinjo, while she was The Dragon of an evil aristocrat trying to overthrow him. He had feelings for her as well, although he remained devoted to Haley.
- And tragically, she was poisoned by her master for her perceived betrayal and died in Elan's arms, and refused to be resurrected if she couldn't be with him.