Emperor Gao maintained the centralized government of his predecessors, and started an enduring bureaucracy based on intellect rather than aristocratic birth. This was in line with the switch from Taoism to Confucianism (under Emperor Wu [140-87 B.C.] who established the Silk Road). By the end of the Western Han, there were 3000 scholars enrolled in the academy for the imperial bureaucracy. The Han established the capital at Chang'an (today's Xi'an) as a part of the Silk Road, through the Gansu corridor.
The empire of the Han extended into Mongolia, Vietnam, and Korea, and the population of China increased to 50,000,000.
Also see Asian History at About.com's Why Did Han China Collapse?
Sarah Milledge Nelson, Brian M. Fagan, Adam Kessler, Julie M. Segraves "China" The Oxford Companion to Archaeology. Brian M. Fagan, ed., Oxford University Press 1996.
Wikipedia Han Dynasty and [formerly at < www.mnsu.edu/emuseum/prehistory/china/early_imperial_china/han.html> Minnesota State University Han Dynasty ]