Various U.S. military departments, including all the major branches of the armed forces, use .mil. The idea is that you can identify the country in which you do business by the domain name you use. But acceptable use differs from country to country. In the United States, each state has its own subdomain, and there are usually subdomains for communities within those subdomains. In Pennsylvania, the state government uses state.pa.us as its primary domain.
Some countries restrict how their domains can be used.
This creates obvious challenges for companies that want to show a local presence in foreign markets. Some entrepreneurs and executives have taken advantage of the TLDs of countries that don't restrict use of their TLDs. If you're a doctor, don't be surprised if you receive a mailer from a company that wants to sell you a domain or even a full Web site ending in .md. So you could be smithassociates.md to clearly identify your profession. This is done by using the TLD of Moldova.