3994 AD is the post-apocalyptic, future Earth setting of Thundarr the Barbarian.
from the opening narration of the animated series:
The year: 1994. From out of space comes a runaway planet, hurtling between the Earth and the Moon, unleashing cosmic destruction! Man's civilization is cast in ruin! Two thousand years later, Earth is reborn. A strange new world rises from the old: a world of savagery, super science and sorcery. But one man bursts his bonds to fight for justice! With his companions Ookla the Mok and Princess Ariel, he pits his strength, his courage, and his fabulous Sunsword against the forces of evil. He is Thundarr, the Barbarian!
For the following: source: Wikipedia, "Thundarr the Barbarian", available under the CC-BY-SA License.
Directly inspired by comic books, with the likes of R.E. Howard's Conan the Barbarian and Flash Gordon, Thundarr the Barbarian is set in a future (3994 AD) post-apocalyptic wasteland divided into kingdoms or territories – the majority of which are ruled by wizards – and whose ruins typically feature recognizable geographical features from the United States, starting in New York City and working itself to Los Angeles, Las Vegas, Mount Rushmore, San Francisco or Washington, D.C.
Other episodes with recognizable settings are located in Central America, while one is in London. Another notable feature of this future Earth is that the Moon was broken in two pieces, but the gravity of the pieces drew them back together, orbiting at roughly the same height as the intact Moon once did. The shattered moon and the ruins of the former human civilization were caused by the passage of a runaway planet (more resembling a comet) between the Earth and the Moon in 1994, which, from scenes shown in the opening sequence, caused radical changes in the Earth's climate, geography and tidal effects. However, by the time period in which the series is set (2,000 years later), the Earth and Moon seem to have settled into a new balance. Earth is reborn in a world of savagery, super-science, and sorcery.