As a soon-to-be-underemployed DHL part-timer, I can add a bit more:
DHL is a wholly-owned subsidiary of DeutschePost which, in turn, probably owes a lot of its success to providing basic postal services in a re-unified, capitalist Germany. DeutschePost prides itself as the world's second-largest employer (after WalMart) and likes to present itself as in sycnh with global, rather than national values.
DHL was founded in the USA; the 'D" in DHL stands for the surname of one of its three founders; nothing "Deutsche' about it. It has never been the dominant player in the US, but is prominent in the rest of the world, primarily through its acquisition of Danzas, International, a Belgian-based freight forwarder which traces its origins to its founders' role as managers of the supply chain for the campaigns of Napoleon Bonaparte.
The "Thoroughbred" containers occasionally seen on US rail movements are a Danzas subsidiary, but I'm nearly certain these are import/export moves. DHL moved domestic shipments within the US almost entirely by highway, using a number of contract carriers.
One minor correction; The 400-or-so "airport facilities" are actually local pickup/delivery hubs. These in turn feed 18 central sorting facilities, of which a hew hub near Allentown, Penna. (built as a successor to the former Airborne Express) and a centrally-located facility developed on the grounds of the former Wright-Patterson Air Force Base near Dayton, Ohio, are the most prominent.The company plans to maintain about 130 offices oriented exclusively towards shipments either originating or destined outside the United States.
What a revoltin' development this is! (William Bendix)