The United States is a member nation of the Paris Convention for the Protection of Industrial Property. As a note, most of developed nations are part of the Paris Convention, including Japan, China, Russia, European nations, Mexico, US, etc.
As a member nation, US applicants may apply for a patent in any of the signatory countries and may file the same patent application within a year in any of the other member nations to receive the benefit of the priority date. Therefore, an applicant may file an application with the USPTO and within a year may directly file an application with other countries and claim the priority date of the USPTO application. This deadline is not extendible; however, an application may be filed in a foreign country after the one-year deadline but will not have the US priority date.
It is important to consider the length of time, costs and protection coverage areas when deciding to file patent applications in other jurisdictions. Typically, directly filing patent applications with a national patent office in each jurisdiction (via the Paris Convention route) is the fastest way to obtain patent protection in the shortest amount of time. However, if an applicant is filing patents in a plurality of jurisdictions the costs of directly filing a patent application may outweigh the speed of obtaining patents.