The Elder Scrolls IV: Oblivion

The fourth Elder Scrolls game set after The Elder Scrolls III: Morrowind. The planes of Oblivion (ruled ultimately by Mehrunes Dagon) open and an onslaught of daedra attempt to take over the province of Cyrodiil, known as the Oblivion Crisis. This crisis was caused by the Mythic Dawn Cult, worshipers of Mehrunes Dagon, who assassinated emperor Uriel Septim VII and his sons. You the player were with the emperor and before he was killed he told you that he had another son Martin Septim, (after the death of the emperor gates to the realm of Oblivion opened) and the daedra attacked and destroyed the city of Kvatch in a deadly surprise attack. Unfortunately, this was the city that Martin Septim was in and he had to be rescued by the player. After this you travel to the fortress/temple of Cloud Ruler Temple home of the Blades, you are then sent on a mission to infiltrate the Mythic Dawn at their secret shrine where you steal the Commentaries on the Mysterium Xarxes, the Mythic Dawn Cult's holy book. Upon your return to Martin, he tells you that you must get other items so that he can perform a ritual to open a portal to Mankar Cameron's (Dagon's second-in-command leader of the Mythic Dawn) "paradise" (his own private world like a miniature plane of Oblivion) which you must enter to find and kill him, the items are a daedric artifact, the blood of a god, a Great Welkynd Stone, and a Great Sigil Stone. Once you have these you are transported to "paradise" where you eventually kill Cameron. Once this has happened you recover the Amulet of Kings from him and you and Martin (with some of the Blades) travel to the Imperial City to crown Martin emperor and light the dragon fires in the temple but once you arrive the daedra, led by Mehrunes Dagon, attack. You and Martin fight your way to the temple where he sacrifices himself to save Tamriel.

The Oblivion Crisis of Cyrodiil occurred around 200 years before The Elder Scrolls V: Skyrim.