[Member 4148]

interstellar empire possibilites will depend on two things: communication and travel time

without high ftl communication and travel, no empire is possible
its possible, just barely, to hold an empire together with travel and communication time measured in weeks
more than that, and it simply won't work long term - if it is six weeks between when a colony rebels and you find out about it, and another six weeks to get any forces there to do something, the rebel colony will be pretty much lost to the empire by the time the troops arrive
with delay measured in weeks, a loose confederacy is about the most that is possible

if travel/communications measured in years due to non-ftl travel, no empire possible beyond local star system

if travel/communications measured in days or less, pick a government - any large-scale government that has worked for a time on earth could work for a time in space - with the proviso that people could flee a long long ways