Judas,
It's a release from T4 and one of only 2 or 3 products from that version of Traveller that are generally acknowledged to be any quality. (Sadly, T4 is more known for its misses than hits.)
Pocket Empires, or PE, resembles a pen and paper version of those computer 'god games' like Civilization. Various rules, charts, tables, and examples are given to guide you through a multi-generational effort to found, build, strengthen, and advance a small or 'pocket' empire far beyond the borders of the young Third Imperium.
PE has high level economic rules, strategic level naval/ground warfare rules, rules for TL advancement, rules for cultural and political manipulation, even rules for dynastic issues within your ruling family. We hadn't had anything like this since CT's Trillion Credit Squadron and never in such nifty detail. That's one reason why folks like PE.
PE presents two 'back stories' as examples. One concerns a 'home grown' pocket empire trying feverishly to rearm and recover past territory in the face of a Third Imperium that is growing more closer. The other story features the one PE suggests as a campaign; a wealthy noble family leaves the Sylean Federation ahead of Cleon's founding of the Imperium. They have no desire to become small fishes in Cleon's big pond and instead set out to create a pocket empire that the Imperium will have to absorb on terms much better to the family.
There is some errata; not much compared to T4's usual offerings but enough to be irritating. The errata can be found on-line however along with some rules fixes.
Have fun,
Bill