Complex sentence: Ajax has historically been one of the most successful clubs in the world; according to the IFFHS, Ajax were the seventh-most successful European club of the 20th century and "The World's Club Team of the Year" in 1992.
Split into simpler sentences: Ajax has historically been one of the most successful clubs in the world. According to the IFFHS, Ajax were the seventh-most successful European club of the 20th century and "The World's Club Team of the Year" in 1992.