15 Times Mortal Enemies Fought Side-By-Side

Tense rivalries often spark some of history’s most compelling alliances. Sometimes, bitter enemies find themselves forced by circumstance to unite against a greater threat. These rare moments of cooperation can change the course of wars, reshape nations, and forge uneasy bonds. Here are fifteen memorable instances when sworn foes set aside old grudges to stand shoulder-to-shoulder on the battlefield—proving that sometimes, necessity really does make for the strangest bedfellows.

1. The Soviet Union and the United States in World War II

Despite profound ideological clashes, the Soviet Union and the United States became unlikely allies to confront Nazi Germany and its allies during World War II. Their combined military and logistical efforts were pivotal in dismantling the Axis powers, particularly after Operation Barbarossa. Both sides collaborated, albeit uneasily, sharing intelligence and coordinating offensives. Their partnership shaped the outcome of the global conflict, though tensions resumed almost immediately afterward, leading to the Cold War. (history.state.gov)

2. Batman and The Joker in DC Comics

Arch-nemeses Batman and The Joker are synonymous with perpetual conflict, yet they’ve occasionally teamed up when Gotham faced even darker threats. In “Batman: The Deadly Duo,” both characters collaborate to rescue Harley Quinn and Commissioner Gordon from a mysterious abductor, navigating a more perilous Gotham City. This storyline delves into their complex relationship, highlighting that even the most bitter rivals can unite against a common enemy. (dc.com)

3. The French and the English Against Napoleon (Seventh Coalition, 1815)

Longtime adversaries, France and England had waged centuries of wars. Yet during the brief period of the Hundred Days, both joined the Seventh Coalition to stop Napoleon’s return. French Royalists fought alongside British forces at Waterloo, striving to end Bonaparte’s reign. These battlefield alliances signified how shifting dangers could momentarily override generational enmity. (en.wikipedia.org)

4. Magneto and Professor X in X-Men Comics

Best known as ideological opposites in Marvel lore, Magneto and Professor X have occasionally set aside their hostile visions to counter existential threats like Sentinels or the Phoenix Force. Their collaborations reveal profound personal history and mutual respect, shining a light on the strengths—and limitations—of rivalry-turned-alliance. These moments test both men’s convictions and the boundaries of trust. (marvel.com)

5. Alexander Hamilton and Aaron Burr in ‘Hamilton’ the Musical

In Lin-Manuel Miranda’s musical “Hamilton,” Alexander Hamilton and Aaron Burr, historical adversaries, are depicted as briefly collaborating to promote the ratification of the U.S. Constitution. This artistic portrayal highlights the complexities of their personal and political dynamics. However, it’s important to note that, historically, Burr did not contribute to “The Federalist Papers,” the series of essays advocating for the Constitution’s adoption. (vpm.org)

6. The Autobots and Decepticons vs. Unicron in ‘Transformers’

Typically locked in unending battle, Autobots and Decepticons temporarily put aside their differences to face the planet-devouring Unicron. Their unexpected alliance—especially notable in the 1986 animated film—emphasizes survival over loyalty. These epic team-ups remain fan favorites, demonstrating that existential threats can unite even sworn metallic foes. (imdb.com)

7. The Hatfields and McCoys During the Civil War

Famed for their deadly feud, the Hatfields and McCoys found common cause during the American Civil War, joining the Confederate Army to fight against Union forces. This rare alliance saw family members from both clans setting aside longstanding animosity for a time. The uneasy truce was short-lived, but it’s a testament to the complexities of survival during war. (britannica.com)

8. Germany and the Soviet Union in the Invasion of Poland (1939)

In August 1939, Nazi Germany and the Soviet Union signed the Molotov-Ribbentrop Pact, a non-aggression agreement that included a secret protocol dividing Eastern Europe into spheres of influence. On September 1, 1939, Germany invaded Poland from the west, and on September 17, the Soviet Union invaded from the east, leading to the partitioning of Poland between the two nations. This unexpected collaboration shocked the world and significantly altered the course of World War II. (britannica.com)

9. Odysseus and Ajax in the Trojan War (Greek Mythology)

Bitter rivals for Achilles’ armor after his death, Odysseus and Ajax nonetheless joined forces for the Greeks during the siege of Troy. While their contention is legendary, necessity mandated their cooperation, reflecting the themes of pride and pragmatism woven throughout mythology. Their alliance underscores the complex interplay between personal honor and collective survival in the epic narratives. (britannica.com)

10. Sherlock Holmes and Professor Moriarty Against Colonel Moran

In Arthur Conan Doyle’s “The Final Problem,” Sherlock Holmes confronts his arch-nemesis, Professor Moriarty, at the Reichenbach Falls. During this encounter, Colonel Sebastian Moran, Moriarty’s chief of staff, attempts to assassinate Holmes. However, Holmes and Moriarty’s struggle inadvertently leads to Moran’s failure, as both Holmes and Moriarty fall into the falls, with Holmes surviving and Moran retreating. This episode highlights the complex dynamics between Holmes, Moriarty, and Moran. (en.wikipedia.org)

11. The United States and the Taliban vs. ISIS-K

Decades of hostility defined the U.S. relationship with the Taliban, yet in recent years, both found themselves targeting ISIS-K as a mutual foe in Afghanistan. While not formal partners, their overlapping interests post-2020 withdrawal have seen some level of cooperation, intelligence sharing, and deconfliction in military strategies. Such makeshift alliances underscore the complicated reality of modern conflict. (cfr.org)

12. Captain America and The Red Skull Against Thanos

In certain comic storylines and adaptations, archrivals Captain America and the Red Skull have experienced temporary team-ups to repel even graver threats—like Thanos and the Infinity Stones. Such uneasy alliances are driven by necessity rather than trust, highlighting the flexible morality of comic book worlds. (en.wikipedia.org)

13. North and South Korea at the 2018 Winter Olympics

The Korean Peninsula remains divided by politics and war, yet during the 2018 Winter Olympics, North and South Korea marched under a unified flag and fielded joint teams in select events. This rare cooperation came amid ongoing tensions, offering a glimpse of potential reconciliation and the power of sports diplomacy. (teenvogue.com)

14. Charles Xavier and Apocalypse in ‘House of X/Powers of X’

In the acclaimed ‘House of X/Powers of X’ storyline, even Professor X unites with ancient adversary Apocalypse to secure the future of mutantkind. This alliance redefines boundaries and demonstrates how cataclysmic events can dissolve even the longest-standing enmities. Their collaboration was as surprising as it was pivotal. Story details.

15. The Mafia and the U.S. Navy During World War II

In a surprising show of pragmatism, the U.S. Navy collaborated with the American Mafia during World War II—most notably through Operation Underworld—to protect East Coast ports from sabotage and facilitate intelligence gathering. This partnership was driven by the need for local knowledge and contacts, demonstrating how desperation can override long-standing hostilities. The collaboration was instrumental in securing vital shipping routes and contributed to the success of Allied operations. (history.com)

Conclusion

History and fiction are replete with unlikely alliances forged in desperate times. These stories reveal that even the deepest rivalries can give way to cooperation when stakes rise high enough. The persistence of such alliances, whether fleeting or transformative, leaves lasting marks on societies, narratives, and our understanding of human—and superhuman—nature.