Empires: a problem of comparative history*
Susan Reynolds
Most historians of empires probably start by assuming that what they are interested in relatively large polities consist a ruling part (the metropolis) and other parts (colonies or peripheries) it dominates as result military conquest political economic bullying, retained governed separately from the metropolis rather than being directly absorbed it. Not all called over centuries, however, have had these characteristics. Surveying some variations characteristics may help deciding be most profitable to compare with what.
Historical Research