In the Copyright Term Extension Act (CTEA) of 1998 (commonly known, derisively, as the "Mickey Mouse Protection Act"), US congress obliged to the Walt Disney Company's lobbying and signed a law that would for the fourth time since 1790 increase the copyright protection length of works, this time to 70 years after the author's death or 120 years after creation for anonymous works.
The Senate Report gave the following justification (in the Purpose section), which I find rather unconvincing:
Such an extension will provide significant trade benefits by substantially harmonizing U.S. copyright law to that of the European Union while ensuring fair compensation for American creators who deserve to benefit fully from the exploitation of their works. Moreover, by stimulating the creation of new works and providing enhanced economic incentives to preserve existing works, such an extension will enhance the long-term volume, vitality and accessibility of the public domain.
In 1790, the copyright duration was of 28 years after creation. It is now almost a century longer.
Is there evidence that a copyright duration of more than 30 years after creation will increase creative output?