Timeline

1944-Godzillasaurus spotted on Lagos island.

1954-An unrelated Godzillasaurus and the Godzillasaurus from Lagos island are mutated into Godzilla I and II. Godzilla I is killed by the Oxygen Destroyer.

1984-Godzilla II appears. Fights and destroys the Super-X. Is trapped inside Mount Mihara.

1989-Godzilla II emerges from Mount Mihara. Fights the Super-X2, Biollante, and is infected by Anti nuclear energy bacteria. Is never seen again.

1990-Spacegodzilla is created and begins a trek to Earth.

1992-The Birth of Godzilla is released by author Kenichiro Terasawa.

1993-Mothra and Battra appear. Battra leaves in the middle of he and Mothra's fight to intercept an asteroid coming for Earth.

1995-Spacegodzilla arrives on Earth. Kills Godzilla, Mothra, Rodan and Baby Godzilla, and goes on to begin sucking Earth dry of energy.

1996-Destoroyah appears. He fights Spacegodzilla and absorbs his blood, turning into his Perfect form. Destoroyah kills Spacegodzilla, but is weakened enough so that the humans are able to kill him with cryo-lasers.

1997-The Earth Union is formed because of the damage caused by Spacegodzilla and Destoroyah, and they begin work on various anti-kaiju superweapons.

2000-Battra returns to Earth and is killed by the combined forces of the new Mothra and humanity. His body is taken for dissection afterwards.

2001-Nuclear weapons are outlawed by the Earth Union, with all existing nukes being gathered up and destroyed.

2005-The Gotengo is built.

2021-Gigan Rex and the Gigan Miles appear. The Gotengo manages to destroy them, but is destroyed as well in the process. Japan reverse engineers the Gigan's remains and uses the technology to become the most economically wealthy nation on the planet.

2200-Japan buys up South America. That same year, the Equal Environment of Earth Union, or EE3 for short, is founded to stop Japan's expansion.

2202-Japan buys up Africa.

2203-The carcass of a 150 meter 3 headed dragon is discovered on the surface of Venus by space explorers. Its DNA is harvested and used to create the Dorats, which become much desired pets.

2204-Learning of the origins of the Dorats, EE3 extremist Chuck Wilson decides to take this chance to enact his own plan to stop Japan's expansion. Alongside his associates Glenchiko and Emmy Kano, he steals an experimental time machine dubbed MOTHER and travels back in time to 1992, telling the nation that Godzilla would destroy the nation in a few years. They journeyed to 1944 alongside 3 1992 people and teleported the Godzillasaurus into the Bering Sea, where they hoped it would die.

They would leave the dorats in the era, and when they returned to 1992, the futurians unleashed King Ghidorah on Japan, hoping to destroy it. Not knowing that Godzilla had still been created by a nuclear submarine in the 1970's, the Japanese government sent a nuclear submarine to mutate Godzilla in the bering sea, only for the monster king to be made even stronger.

He would then fight King Ghidorah while Emmy betrayed the other members of her group, teleporting their ship in front of Godzilla, who destroyed it. Godzilla defeated King Ghdiroah and then began attacking Japan himself, forcing Emmy to go to a new timeline and revive Ghidorah as Mecha-King Ghidorah. The 2 fought in 1992, and Mecha-King Ghdiorah was successfully able to carry Godzilla out to sea before returning to 2204.

Author's note: No, the heisei Godzilla timeline is not a time loop, it is stated by official sources that 3 timelines were created by the time travelling in the movie.

Timeline 1: The futurian's timeline, where Godzilla never recovers from the ANEB and is never seen again after Godzilla vs Biollante. This is the timeline I just covered, and the timeline where Jet Jaguar and M11 come from in this fanfic.

Timeline 2: Mecha-King Ghidorah timeline. The timeline Emmy left behind when she went to create Mecha-King Ghidorah. In this timeline, Godzilla destroyed Japan entirely after defeating King Ghidorah, rendering the nation uninhabitable.

Timeline 3: The main timeline. This is the timeline of all of the main heisei movies from Gojira to Godzilla vs Megalon 2023.

I hope this clears things up.