Two Kinds Of Series

Many a fictional series is built on continuing characters like Holmes and Watson or like Poul Anderson's Manse Everard of the Time Patrol. (In the appropriate period, Everard meets Holmes and Watson. Events of two series intersect.)

A future history series is built not on continuing characters but on successive historical periods. In Robert Heinlein's Future History, as in Anderson's Psychotechnic History, a handful of characters appear at most twice but the series as a whole is not about them. 

However, Anderson's Technic History almost uniquely incorporates two long character-based series into different future periods. Larry Niven almost matches this with two sets of characters in his Known Space future history. In the second main section of Anderson's Technic History, we read:

eight instalments in three volumes about Captain Dominic Flandry;

a later-written trilogy of novels about the younger Flandry as Ensign, Lieutenant and Commander;

two later novels in which Flandry has become an Admiral, first Vice, then Fleet.

Eight volumes: it seems as if the forward march of history has halted and has been replaced by the career of a single individual. 

However:

two non-Flandry instalments, a story and a novel, are set during the Flandry period;

there is a historical turning point during Flandry's lifetime;

if we continue to read the Technic History, then we do eventually reach that post-Imperial "Long Night" that Flandry had resisted for so long;

Technic civilization ends but human interstellar history continues in subsequent civilizations.