Fallout season 2 ending explained: who started the Great War?

The finale ends with Caesar’s Legion fracturing as Legate kills a witness and crowns himself Caesar, while the Lucky 38 scenes reveal House confirming that Cooper delivered a cold fusion diode to the Enclave. On the Strip Maximus and Lucy survive a Deathclaw attack as the New California Republic arrives, and the Ghoul finds Barb and Janey’s cryopods empty, with a postcard that points him toward Colorado.

Cooper is revealed to have unwittingly given the diode to the Enclave, an action Robert House says kickstarts the nuclear disaster known as the Great War. After a cryptic phone call from House at the airport, Cooper is arrested on the authority of the House Un‑American Activities Committee; his fate is left unresolved and season 3 is expected to fill in how he became the Ghoul.

The episode also confirms Hank’s experiments: he used Congresswoman Diane Welch’s severed head as the "gold standard" personality for microchips, implanted a chip in himself, and says the surface was always his experiment.

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