The United States, in an attempt to prevent corruption among military personnel in charge of purchasing, it's illegal for anyone to give anything worth more than $20 to a soldier. Exceptions can be made if there is a formal, and time consuming, ethics review. This proved to be a problem as people began sending goodies to U.S. troops wounded in Iraq and Afghanistan. It caused many an embarrassing moment at military hospitals, as well wishers were told they were breaking the law with the gifts they were trying to give to recovering troops. So the law was changed (after being ignored quite a lot in the last four years.) In recognition of that, the law was made retroactive to September 11, 2001.