Timeline

1954
the "Original Godzilla" surfaces in Tokyo, and attacks the city. The JSDF eventually kills the beast by luring it into a trap and carpet-bombing it.

1974
The "First Godzilla" resurfaces in Tokyo. It would eventually be theorized that this Godzilla was the offspring of the first Godzilla. He is smarter, and wreaks havoc on the entire city without taking much of any damage, and, after destroying the city entirely, retreats back into the ocean.

1975
Godzilla resurfaces and attacks Tokyo once more. This time, the JSDF are prepared, and have Maser Cannons ready to retaliate. The Maser Cannons have a minimal effect on Godzilla, but they are able to draw him away from the city. As Godzilla gets further from the city, Anguirus arrives and attacks Godzilla. The two of them fight until they reach Mt. Fuji, and Anguirus lures Godzilla to the top, in an attempt to get him to fall into the volcano. However, Godzilla realizes this, and charges Anguirus, pushing him into the volcano. Anguirus, however, bites Godzilla's leg and holds on, causing Godzilla to fall into the volcano with him.

1977
Two years after the events of Godzilla VS Anguirus in 1985, Godzilla and Anguirus return from within the volcano, and seem to be friends now. The two go their separate ways, and Godzilla heads to the ocean. However, before he can reach the ocean, he is attacked by Baragon. The two clash for a short while, and then Godzilla kills Baragon when their fire and atomic beams collide, but Godzilla's overpowers Baragon's. Godzilla then retreats to the ocean.

1978
A meteor crashes on Earth, and it eventually hatches, and from within it comes King Ghidorah. He begins to wreak havoc on the nearby city of Shanghai. Mothra sees this happening and goes to find the "two strongest monsters she knows" for help. She finds Godzilla and Rodan fighting, and tries to get their attention. She fails to convince them, and leaves. Before long, King Ghidorah arrives and attacks Godzilla and Rodan. Rodan stands by as Godzilla and Ghidorah clash, and eventually Godzilla is downed. Rodan flees, but King Ghidorah shoots him out of the sky with his gravity beams.

Rodan crashes near Mothra, and after a brief talk, Rodan agrees to help her. The two of them fly into battle, and temporarily drive King Ghidorah away. The three monsters hatch a plan to defeat Ghidorah. Godzilla swims away, and when Ghidorah returns, Rodan and Mothra use their beam attacks to make Ghidorah follow them. The two of them lead him to Antarctica, where Godzilla is waiting. Then, Mothra and Rodan fire their beams at Ghidorah's wings, knocking him out of the sky. He crashes on the ground, and Godzilla uses his atomic breath to break the ice around Ghidorah, who sinks into the water, which quickly re-freezes, trapping Ghidorah. The three monsters then go their separate ways.

1979
Godzilla has not been seen since he fought alongside Rodan and Mothra against King Ghidorah. Then, a monster that looks slightly different than Godzilla is seen fighting Titanosaurus. Godzilla unleashes his atomic breath onto Titanosaurus' stomach, causing it to explode, killing Titanosaurus. One of the people watching remarks that Godzilla's atomic breath is blue, not yellow. The Godzilla approaches Tokyo, and attacks the city. Before long, the real Godzilla arrives, and attacks the fake. After maintaining a lot of damage, the fake Godzilla reveals itself as Mechagodzilla, and attacks Godzilla. A long fight commences, which lasts for three days in three different cities. Godzilla eventually overpowers Mechagodzilla, tearing his right arm off, and ripping his head off of his shoulders.The headless Mechagodzilla falls to the ground, and Godzilla roars triumphantly before going back to the ocean.

1980
A science experiment creates Hedorah, who flies to San Diego and attacks it. Godzilla arrives and attacks Hedorah, and quickly kills him.