Toei was originally a movie company that specialized in samurai period dramas, and even in their first TV cartoon production, they planned to produce something with a period theme. The show was an adaptation of the boy-ninja story genre that existed in Japan and was adapted into an African story. However, it was the era of the space race, and it was science fiction shows like Astro Boy, Eighth Man and Gigantor that attracted the attention of American broadcasters and distributors. In fact, "Wolf Boy Ken" was also purchased by a major program distributor, but it was never aired in the United States. This distributor sold many American-made TV movies to Japanese broadcasters, particularly Nippon Kyoiku Television (now TV Asahi), which was a client of the American TV distributor. Toei was the television network's largest shareholder at the time, so they only bought Ken as a congratulatory　purchase for Toei.

It was hoped that exporting television cartoons to the U.S. would consistently earn dollars, but Japanese cartoon producers soon learned that it didn't really work out that way. To begin with, Astro Boy weren't really making as much money in dollars as they thought they would. NBC bought the second year installment of the show, but not the third year's. Tezuka planned "Kinba the White Lion," inspired by Disney's "Bambi", and NBC once again made a deal with Tezuka, but then the new guidelines for purchasing TV programs in the U.S. came into effect, and a result of that was the export of animated TV programs from Japan was hobbled by these guidelines. Speed Racer (produced by Tatsunoko Productions, led by Tatsuo Yoshida, who had been a rival of Tezuka's during his days as a manga artist) in 1967, was the last Japanese cartoon show, before the blank period of anime in the U.S. was coming. soa natural?

Yours: It was hoped that exporting television cartoons to the U.S. would consistently earn dollars, but Japanese cartoon producers soon learned that it didn't really work out that way.

Correction: Japanese cartoon producers hoped that exporting television cartoons to the U.S. would consistently earn dollars, but they soon learned that it didn't really work out that way.
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Yours: To begin with, Astro Boy weren't really making as much money in dollars as they thought they would.

Correction: To begin with, Astro Boy wasn't making as much money as they thought it would.
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Yours: NBC bought the second year installment of the show, but not the third year's.

Correction: NBC bought the second installment of the show, but not the third.
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Yours: Tezuka planned "Kinba the White Lion," inspired by Disney's "Bambi", and NBC once again made a deal with Tezuka, but then the new guidelines for purchasing TV programs in the U.S. came into effect, and a result of that was the export of animated TV programs from Japan was hobbled by these guidelines.

Correction: Tezuka planned "Kimba the White Lion", inspired by Disney's "Bambi", and NBC once again made a deal with Tezuka, but when the new guidelines for purchasing TV programs in the U.S. came into effect, they resulted in the export of animated TV programs from Japan being hobbled by these guidelines.
(You can put the commas either outside of or inside of the quotation marks. Outside is British English, inside is American English. Also, it's not a spelling error on my part! 'Kimba' is romanized as 'Kimba' and not 'Kinba', even though 'Kinba' would technically be correct.)
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Yours: Speed Racer (produced by Tatsunoko Productions, led by Tatsuo Yoshida, who had been a rival of Tezuka's during his days as a manga artist) in 1967, was the last Japanese cartoon show, before the blank period of anime in the U.S. is coming.

Correction: Speed Racer, produced by Tatsunoko Productions, led by Tatsuo Yoshida, who had been a rival of Tezuka's during his days as a manga artist, was released in 1967 and it was the last Japanese cartoon show before anime left the U.S./disappeared from the U.S.
(alternative wordings might be 'the disappearance/departure of anime from the U.S.' and things like that but saying "blank period of anime in the U.S." makes it sound a bit contradictory. Like, it's a blank period, but it's still in the U.S.?)
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I recommend breaking up your last two sentences as they're really long. I put your original sentence and then mine so you could compare the minute changes I made