Quoting Rohan McLeod (rhn@jeack.com.au):
Being curious about the difference between ".us" and " " ; I discovered
"Why choose .US?
[Snip sales fluff. ;-> ] The DNS namespace grew rather than being planned, is the real explanation. For historical reasons, we've ended up with two-letter country-code TLDs (ccTLDs) like au. and us. alongside three-and-more-letter generic TLDs (gTLDs) such as com., org., net., gov., mil., aero., coop., info., mobi., and so on. http://en.wikipedia.org/wiki/GTLD http://en.wikipedia.org/wiki/Country_code_top-level_domain And most recentlly, we have internationalised ccTLDs (IDN ccTLDs)... http://en.wikipedia.org/wiki/Internationalized_country_code_top-level_domain ...but I digress. The wide and lasting popularity of the major gTLDs from early on has made a reorg awkward and thus unlikely. For example, US Federal government domains _should_ have been grouped under gov.us. but instead emerged under gov. Likewise, US nonprofits _should_ have been in org.us. but instead sprouted up in org, and commercial firms should have been in com.us. but used com. instead. And now, of course. com. and other primary gTLD namespaces are popular... because they're popular. The us. ccTLD is primarily used by USA non-Federal government entities (mostly cities and counties). Even there, it's often spurned as undesirable namespace. E.g., my local town (Menlo Park, California) owns menlo-park.ca.us. but is mostly known by menlopark.org. (Please note that I've consistently used, above, the full-qualified form of domain names, i.e., ending in the period that denotes the namespace root. The closing dot is often omitted but is technically necessary to avoid ambiguity, and sometimes is required for correct operation of software.)