Complex sentence: WPS maintained an enormous user base throughout the late 1980s and early 1990s but when Microsoft Office 95 and Windows 95 were introduced into the Chinese market, the influence and sales of WPS went into steep decline.
Split into simpler sentences: WPS maintained an enormous user base throughout the late 1980s and early 1990s. When Microsoft Office 95 and Windows 95 were introduced into the Chinese market, the influence and sales of WPS went into steep decline.