In the beginning there was Disney
And Japan said; "That's awesome, we're copying it."
Thus began the first age of anime.
Japan populated its animated world with feature films in the same vein as the Disney pictures of old. And they saw it was good.
Then came television. And the age of the feature film declined.
Then there was Ashita no Joe. It was the greatest sports manga and anime [arguably] of all creation. And the true sports genre was born. And manga adaptation was born. And televised serialisation was born.
Then, [with heavy influences from the West's space race, moon landings etc.] there was Gundam.
And Japan said; "giant fighting robots are awesome."
And mecha was born. And it Japan saw it was good, and has loved it to this day.
And at this time, one who was and is known as [arguably] the greatest known animator/director of all time created Nausicaa of the Valley of the Winds. (Kaze no Tani no Nausicaa).
And Studio Ghibli was created. And it later became one of the most widely recognised and respected animation studios in the world.
And the anime feature film was reborn. The film Akira in particular brought significant international recognition to the genre.
And, also, at this time, a son was placed in the garden. His name was Goku. And there were Dragonballs. It was awesome.
And the (modern) martial arts/shonen genre was born.
And shortly after, a daughter was placed in the garden, and there was Sailor Moon.
And the (modern) Magical Girl/shojo genre was born.
And, at the same time, from the west came two things; the video cassette and the interactive computer game. And the visual novel came into creation, immediately followed by the eroge. [due to absent censorship regulations]
Thus, explicit content came to be animated and put on video, and the H genre was born.
These [relatively] simultaneous events were considered a golden age of anime. And Japan revelled in its own creation, and thought it beautiful, and brought in the crops while the sun was high. Thus, what came to be known as Otaku culture was born.
But it was not over yet.
Descending from the animated heavens on wings of steel-
Then there was Evangelion.
(TBC in Pt. 2)