Notions of 'civilisation', 'country', 'state', 'people', 'nation' and so forth are constantly shifting targets, and so to assert a continuity is meaningless if the underlying definitions change over time. This exchange between /u/handsomeboh, /u/keyilan and myself gets a version of this across in brief, but if you (or anyone else reading this) would like me to elaborate I'll gladly do so.