What Is the Thucydides Trap?

The concept of the “Thucydides Trap” appears often in modern discussions of U.S.-China relations, but its roots date back to ancient Greece. At its core, the term describes the idea that when a rising power begins to challenge a ruling one, tensions grow, fear sets in and the risk of war increases.

Thucydides (c. 460 B.C.-c. 400 B.C.) was an Athenian general and historian who wrote about the Peloponnesian War between Athens and Sparta in the fifth century B.C. In The History of the Peloponnesian War, he wrote, “The growth of the power of Athens, and the alarm which this inspired in Lacedaemon (Sparta), made war inevitable.” 

According to Harvard political scientist Graham Allison, who coined the phrase “Thucydides Trap” in 2012, Thucydides focused on the deeper forces driving the war. In a 2015 article in The Atlantic, Allison wrote that Athens’ growing influence made it more confident and more sensitive to slights, while Sparta saw Athens’ behavior as unreasonable and threatening. 

Allison brought the term into modern foreign-policy discussions through research at the Harvard Kennedy School’s Belfer Center. His team studied 16 cases from the past 500 years where a rising power challenged an established one. All but four led to war. Allison summarizes these examples and expands on the concept in his 2017 book Destined for War: Can America and China Escape Thucydides’s Trap?.

Allison points to the 1914 assassination of Archduke Franz Ferdinand, which helped start the chain of events that led to World War I, as an example of how a relatively contained occurrence can lead to a major conflict. The cases also include France challenging Habsburg dominance in the 17th century, which contributed to the Thirty Years’ War, and Japan’s early 20th-century rise against the U.S. that culminated in the Pacific War during World War II. 

The Thucydides Trap has become a recurring theme in high-level diplomacy. Chinese President Xi Jinping has brought it up in meetings with U.S. presidents and leaders, including Barack Obama in 2015, Joe Biden in 2024 and Donald Trump in 2026.

During a 2015 summit in Seattle, Xi said, “There is no such thing as the so-called Thucydides Trap in the world.” But he warned that major powers can create one if they “time and again make the mistakes of strategic miscalculation.”

“Can China and the United States transcend the so-called ‘Thucydides Trap’ and forge a new paradigm for major-power relations?” Xi repeated during a 2026 meeting with Trump in Beijing. 

Allison and many political leaders stress that the Thucydides Trap is a warning that rising tensions make conflict more likely—but not unavoidable. 

The Belfer Center case studies in which war was avoided include the United States overtaking Britain in the early 20th century because Britain stepped back rather than confront the United States directly. The Cold War rivalry between the U.S. and the Soviet Union did not turn hot thanks to deterrence and diplomacy. And in the 15th century, Portugal and Spain managed their conflict through treaties instead of fighting. 

“When the parties avoided war,” Allison writes in The Atlantic, “it required huge, painful adjustments in attitudes and actions on the part of not just the challenger but also the challenged.”