The US Postal Service supplies tracking numbers for packages traveling internationally. Unfortunately, tracking services as rendered through the USPS website stop once the package leaves the US. Strangely, this includes the exit as well. The USPS sometimes scans/logs packages when they leave facilities, but not every time. Typically they only scan a package when it arrives at a new location, as is the case with international packages leaving the country... the exit is not logged, and once the package leaves the port city, tracking sort of "dead ends".
Once a package has left a US port city (San Francisco, Los Angeles, New York, etc.) it will transit to the destination country and enter into a customs/entry process in that country. Once customs clears the package it will be handed off to whatever domestic postal service operations there are in the destination country, and if that domestic postal service has a package tracking service, the same tracking number can be used to track the package domestically. Until the domestic carrier receives the package from domestic customs, the package will be in a sort of limbo state, with no visibility.
Equally frustrating is the fact Dangerous Things can do nothing about the idiosyncrasies of each country's domestic customs and postal delivery services. Contacting your local postal service is your best bet at discovering the fate of your package.
Here is a short example list of international postal service tracking pages;