Titan

"It was beautiful. Titan was like most planets, 20 miles, not enough to go around. And when we faced extinction, I offered a solution." "Genocide." "At random. It would be fair, for rich and poor alike. They called me a madman. And what I predicted came to pass."

- Thanos and Doctor Strange

Titan is the wrecked homeworld of Thanos.

Destruction
Home to an eponymous race of beings, Titan was once a rich, lush world. It was plagued by overpopulation however which caused a drain on its resources and sent the Titan race hurtling towards a societal cataclysm. The outcast Thanos proposed randomly killing half the planet's population as a way to preserve their finite resources but his plan was rejected as too extreme. The predicted catastrophe then hit Titan, causing the mass extinction of most of the planet's lifeforms. The once green and blue world turned burnt orange and brown with the broken remains of Titan society littering its surface. On a planetary scale, Titan was left eight degrees off its axis with its gravitational pull being "all over the place". Convinced that his plans could have saved his homeworld, Thanos became dedicated to wiping out half the life in the universe so as to spare other planets from sharing the fate of his own.

Arrival of Earth's Heroes
In early 2018, following his retrieval of the Space Stone, Thanos sent the Black Order to Earth with orders to bring the Time and Mind Stones to Titan. In Ebony Maw's attempt to pry the former from Doctor Strange, he was slain by Iron Man and Spider-Man. The three humans then seized control of Maw's Q-Ship which crash landed on Titan. After meeting half the Guardians of the Galaxy, the six agreed to work together to defeat Thanos.

Battle of Titan
Once the warlord arrived, he briefly explained his world's history to Strange before the heroes, bolstered by the independently arrived Nebula, engaged him. The seven managed to immobilize Thanos long enough for Mantis to subdue him with her powers before they attempted to pry off the Infinity Gauntlet. When Mantis felt that Thanos was in mourning however, Peter Quill deduced that he had killed Gamora and attacked the Titan in a rage breaking Mantis's concentration. Using the Power and Space Stones, Thanos ripped apart Titan's moon and sent it hurtling at his foes. The sole one to dodge the debris, Iron Man personally engaged Thanos only to be defeated forcing Strange to barter the Time Stone for Stark's life. His prize secured, Thanos departed.

As the heroes regroup, Thanos completed the Infinity Gauntlet and used its powers to fulfill his goal. Of those on Titan, only Nebula and Iron Man were spared leaving them stranded on the dead planet.

Trivia

 * In the comics, Thanos' homeworld is the real-life moon of named, rather than a fictional planet of the same name in another solar system.