It doesn't matter. The US just has one vote on the UN's WIPO http://en.wikipedia.org/wiki/World_Intellectual_Property_Org.... I've no idea how you get 185 member states to decide that 50 years after death is a good minimum length for copyright. Imagine the good they could do if they agreed on anything useful!
The one vote of the US doesn't matter. Historically, the US has been the biggest funder of the UN, and traditionally the organisation is dependent on the dues of the US being paid. The US tends to use this as a bargaining chip, which is an awful lot more powerful than just one vote.
http://en.wikipedia.org/wiki/United_States_and_the_United_Na...
Bear in mind that we're not even talking about US diplomatic efforts here, which typically sway many nations in exchange for other favours.
Historically, the copyright lobby has been even more successful in lobbying the state department to bully other nations to adopt draconian copyright laws than it has been in lobbying our own congress to adopt such laws.
