Three Major American Future Historians

In my teens, I rated James Blish more than Robert Heinlein and Heinlein more than Poul Anderson - Larry Niven was not around yet - but I had not yet read enough Anderson and he wrote a lot more after that.

I hope to have demonstrated that Anderson's Technic History is an ultimate future history series, surpassing Heinlein's in:

number of installments;
length of time covered;
number of historical periods covered;
volume of space encompassed;
interesting characters;
continuing characters;
series within the series;
alien races;
extraterrestrial environments;
analyses of historical processes;
quality of writing.

Heinlein's Future History is, as a series, complete in four volumes because Volume V is a short appendix that does not advance the fictional history. Blish's major future historical work, Cities In Flight, a tetralogy, might be classed as a truncated future history because:

it holds up well as a future history series until somewhere in Volume III but, after that, the antiagathics are keeping a small group of characters alive indefinitely so the reader loses track of the centuries;

the universe is destroyed and new creations begin at the end of Volume IV.

The Technic History, many volumes longer, addresses an indefinite future.