The Hiatus was a prolonged period of time during which interstellar travel and trade between the planets humanity had colonized came to a halt.
When the Hiatus came to an end, more and more human worlds began to reestablish space trade and make contact with each other again, leading to a new age of exploration and colonization. (RCN1)
The Hiatus in human civilization occurred when the first tier of star systems colonized from Earth revolted against the home world. The war was fought with asteroids accelerated to slam into planets, distorting the crust and killing all but a few percent of those living on those worlds before the war started.
It was a millennium before mankind returned to the stars, and the return came from second- and third-tier colonies, worlds like Cinnabar and Pleasaunce which had been too minor for either side to bother destroying. No one today could tell what the Earth looked like before the Hiatus, because the continents had died along with those who lived on them. (RCN3)