The 1963 death of Rikidozan, who dictated the pro-wrestling in Japan, brought a drastic change to the industry. Hiro Matsuda, who had not been allowed by Rikidozan to wrestle in Japan, announced his return in 1964 and started wrestling for JWA two years later. Meanwhile, JWA was continued by the four infamous directors: Yoshinosato, Michiaki Yoshimura, Kokichi Endo, and Toyonobori, who would be later kicked out and form Tokyo Pro-Wrestling with Antonio Inoki.
Isao Yoshiwara was having a problem with the treasurer Endo and finally split from the company. In October, 1966, he announced the starting of a new pro-wrestling organization: International Wrestling Enterprise. It was Yoshiwara who helped Matsuda to return home, and he had the opening series in January of the following year with Matsuda as the top star of the new company. The first series was co-promoted with Tokyo Pro-Wrestling, which would eventually close down later in the year.
With no television coverage or big name stars, IWE was having poor attendances for its card, and Yoshiwara had to let Tokyo Broadcasting System to take the control of the company. TBS made several wrong decisions including assigning Great Togo as the booker, which caused various problems including Matsuda's departure from the company.
After split with Togo and his American wrestlers, Yoshiwara went to Europe for the source of the foreign talents. The first IWA world heavyweight championship was won by Bill Robinson, a talented British wrestler who was not yet a familar face in North America. Robinson became the first (and the only?) foreign wrestler to be the top man of a pro-wrestling organization in Japan. Also, through IWE's relationship with the European promoters, Japanese fans were introduced to not only the orthodox style of European wrestling but also many stars who were then unknown to North American fans including Billy Joyce, Albert Wall, and Monster Roussimouff, a future legend who is better known as Andrè the Giant.
In 1970, IWE signed a working agreement with Verne Gagne's AWA, and IWE finally had a stable source of North American talents while keeping relationship with Europe. This would eventually lead Robinson and Roussimouff to get attention from North American promoters. Without IWE, there may not have been the legend of Andrè the Giant.
Also in the same year, IWE had the first ever steel cage death match in Japan, with Rusher Kimura, who would be later known as "Master of Steel Cage", defeating Dr. Death (Moose Morowski). Two years prior to this match, IWE had the first hair match in Japan when Thunder Sugiyama & Kimura defeated Tank Morgan & Dory Dixon with the team leader Morgan shaving his head (though he was almost bald already at the time anyway). While keeping the classic style of wrestling with the wrestlers from Europe and AWA, they also started having death matches (e.g. the cage matches mainly by Kimura, Indian strap matches with the first one being Great Kusatsu vs Wahoo McDaniel in 1973, etc.).
In spite of his creative idea, Yoshiwara never had a big name Japanese star, and he was also known as someone who was too nice to be a good businessman. He lost a lot of money through the deal with Gagne. Eventually IWE would lose its television spot and finally closes down in 1981. Kimura, Animal Hamaguchi, and Isamu Teranishi joined New Japan to start the famous "inter-promotional" feud, and others such as Mighty Inoue, Ashura Hara, Goro Tsurumi, etc., went to All Japan. Yoshiwara would be eventually hired by New Japan as a booker but passed away in 1985 at the young age of 55.
It was IWE that brought Bill Robinson and Andrè the Giant to North America, made the death matches famous almost two decades before FMW was founded, started using entrance music for the first time in Japan even before Mil Mascaras made his "Sky High" famous, and showed interest in another non-Japanese grappling style such as sambo almost a dacade before New Japan and UWF started paying attention to it. IWE was indeed the most innovative organization in the history of puroresu.
* Sources: various Japanese magazines, Dr. Mick's Showa Puroresu Research Room, etc