Note: This chronology heavily relies on the statement "~ years after the Bacterian war" mentioned in a respective game's storyline. Every "Bacterian war" is considered as the 3rd Bacterian war - the final showdown against the head Bacterian, so this chronology can be wrong if the "Bacterian war" mentioned in a game was actually referring to other wars with the Bacterian army. Also, games with the same name (such as Salamander and Salamander (MSX) are considered as events occurred in the same year in this chronology. This adds the chance of being wrong too, but currently this is the best what a Gradius fan can do, considering lack of information about these problems from official sources.
Currently, Nemesis (GB), Gradius: The Interstellar Assault, Salamander (arcade) and Life Force have the problems listed above.

There is a 6000 year difference between the Gradian and Earth calendars.

Wreek power era

  • 6644: The Northern Cross War takes place. A massive Bacterian fleet comes from the future and kidnaps the young James Burton, who is subsequently rescued and brought home by the pilot of the Vixen ship, which also came from the future. (Nemesis 3, second half)
  • 6645: As a result of the Northern Cross War's battles, the Wreek population is almost decimated due to the radiation left in their dwelling place on Gradius' southern hemisphere; in response, the Gradian Empire enacts a protection policy for the Wreekians.
  • 6658: The First Bacterian War takes place. The Bacterians launch their first attack against Gradius, but are defeated by a seventeen year old James Burton piloting the Vic Viper. (Gradius)
  • 6658: A Bacterian squadron ambushes a group of Gradian ships, but the Vic Viper escapes the attack and eventually destroys the squadron in a counterattack. (Gradius: The Interstellar Assault)
  • 6660: The Second Bacterian War takes place. Led by Gofer, the Bacterians once again attack Gradius but are defeated. Even though Gofer is destroyed, his fragments scatter throughout the cosmos. (Gradius II)
  • 6660: Dr. Venom is appointed the Director General of the Space Science Agency.
  • 6664: The Battle for Antichthon takes place. In the end, Venom is caught and arrested for a failed coup d'état, then subsequently banished. (Gradius ReBirth)
  • 6665: Venom escapes the prison planet Sard and conspires with the Bacterians, whom turn him into a cyborg in order to maximize his Wreekian powers.
  • 6666: The Silent Nightmare incident takes place. Venom and his Wreekian fellows launch a full-scale attack against Gradius. James Burton is sent to fight Venom's forces with the Metalion spaceship. After a fierce battle, Venom dies in combat with the destruction of his fleet. James is crowned as "Emperor Lars XVIII". (Nemesis 2)
  • 6709: The Crush-Blow Operation takes place. Following a centuries-old prophecy, Latis is surrounded by the Zelos Force, so Emperor Lars XVIII orders an assault to liberate Latis. The pilots Iggy Rock and Zowie Scott fight the enemy forces and uncover pieces of the prophecy, discovering a revived Dr. Venom is behind the attack. Venom is once again defeated and the force surrounding Latis is destroyed. (Salamander (MSX))
  • 6718:  James Burton passes away at the age of 77 and, with this, the Wreekians are officially declared extinct.

Sub-space era

  • 6809: The Bacterians amass a large fleet with the intent to travel to the past and kill James Burton while he's a child. David is sent in the Vixen spacecraft to intercept the Bacterian forces. (Nemesis 3, first half)
  • 6840: The Third Bacterian War takes place. The Dark Force, led by Bacterian the creator and central system himself, launches a full-scale assault against the Gradius forces and almost annihilates them. The Vic Viper is once again sent into battle, reaches the dwelling place of Bacterian and destroys him but not before it states that as long as humans and their desires exist, so will he. (Gradius III)
  • 6842: A huge creature named Life Force tries to devour Gradius and Latis in an attack that is similar to the Salamander War. (Life Force)
  • 6850: A planetoid by the name of Special Force is created but is ultimately destroyed by Vic Viper and Lord British. (Salamander (PCE))
  • 6852: The Hyper Space Fighter "Alpinia" is constructed. In the wake of this achievement, a mysterious fortress appears and starts devouring all planets in its path, with its ultimate aim being to destroy Gradius. The new Alpinia is sent to join the Vic Viper and Lord British in an attack on the enemy fortress and their combined effort is a success. (Solar Assault)

Gaiden era

  • 6860: The Fourth Bacterian War takes place. A piece of Gofer reaches a distant planet and the reformed entity transforms it into a battleship which immediately proceeds to attack Gradius. The Vic Viper is sent to fight the enemy forces and after the destruction of the revived Gofer, the planet reverts to its original state. (Gradius IV)
  • 7012: The Salamander Force is revived by a mysterious entity named Doom. The Gradius Empire sends the Vic Viper and Super Cobra into battle against the new enemy and they successfully destroy it. (Salamander 2)
  • 7040: A science vessel mysteriously disappears after approaching the Evil Range, an off-limits Dark Nebula. Shortly after this, a powerful evil force emerges from the Dark Nebula and attacks the Gradius colony planets. The Gradius army is overpowered and 99% destroyed by this enemy force. In a desperation counterattack, the four hyperspace fighters Vic Viper, Lord British, Jade Knight and Falchion β are sent to the Dark Nebula and they successfully destroy the source of the invaders there. (Gradius Gaiden)
  • 7240: A piece of Bacterian lands on planet Lamiless and transforms it into a fortress. The Vic Viper is sent to the planet and liberates it from the Bacterian influence. (Gradius Galaxies)
  • 8010: The Fifth Bacterian War takes place. Venom uses Bacterian cells — either from Gofer, Bacterian, or himself — to recreate his fleet. The pilots of the Vic Viper T-301 and Alpinia team up and use a time warp in order to stop Venom with their past selves. (Gradius V)
  • 8100: After a final offensive, the Bacterian Empire is destroyed for good. The Gradius Empire is dissolved and the Gradius Union is created to replace it.
  • 8120: After obtaining ancient Bacterian and Gradian technology, the Lars Empire is created.
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