Turning Points

One passage in Poul Anderson's Mirkheim and two events in Sandra Miesel's Chronology of Technic Civilization enable us to identify three turning points in the History of Technic Civilization:

(i) the transition from Western to Technic Civilization;
(ii) the failure of the Polesotechnic League;
(iii) the failure of the Terran Empire.

(i) In the twenty first century, O'Neill colonies were:

placed at the Lagrangian points sixty degrees before and behind the Moon;
the first human dwellings off Earth;
the sites of entire new industries, reviving free enterprise;
a source of new ways of thinking and living;
"...together with the alloying of formerly disparate Terrestrial societies...," (Rise Of The Terran Empire, p. 139), the beginning of Technic Civilization.

This passage and "The Saturn Game," about light sail ships exploring the Solar System, are our only two sources of information about the twentieth century in the Technic History timeline.

In the twenty second century, interstellar travel makes the O'Neill colonies redundant but they are not vacated immediately and are still inhabited when the Polesotechnic League holds a Grand Council in the colony called Hiawatha three centuries later - which will lead us to (ii).