I think Tyrann is modeled after the Monguls took over china once.
Distance from Earth
There is a typographical error in the book: Tyrann must be 500 parsecs [not 500 light-years] from Earth, because that's the distance to the Horsehead Nebula [and Tyrann is one of the Nebular Kingdoms].
This also suggests that Tyrann was not in the Sirius Sector, but in a neighbouring Sector - probably the Rigel Sector mentioned in Pebble in the Sky.
concurrence with "Dune" (1965)
An echo of a desert-planet that gets to rule the known universe, feudally and the practice of water-redestillation and conservation from human excrements occurs in Frank Herbert's "Dune" written later and published in 1965. Who knows of secondary research to confirm or deny this suggestion? Thomas Körtvélyessy 17:25, 27 July 2007 (UTC)