Complex sentence: Playtex Products had continued to erode Tampax's' market share throughout the late 20th century to the point where the two companies had divided the market almost evenly by the late 1990s.
Split into simpler sentences: Playtex Products had continued to erode Tampax's' market share throughout the late 20th century. The two companies had divided the market almost evenly by the late 1990s.