Exporting from the US is a privilege, not a right. This is make especially clear when exporting something that the US Government has decided to regulate in some way. There are many export licenses available from large number of government agencies. Although this can be daunting the look at, it is considered the responsibility of the exporter to identify the proper government agencies and seek them out prior to shipping. This is one case where ignorance of the law is no shield.
One of the most common export licenses is for defense and security related articles. This export license is offered by the US Department of State through the Directorate of Defense Trade Controls (DDTC). Depending on the nature and duration of this export, various export licenses can be obtains. The most common license sought is a DSP-5 for temporary or permanent export of defense-related items to a single end-user. Note this export license does not allow the buyer the right to re-transfer the article without obtaining prior permission. This permission is typically sought though a General Correspondence (GC).