“Once, long ago, the world was unified. Oh, there were many nations, to be sure, and many cities, but rare indeed were those that could not talk to the others. The world entered an age of progress that has never been seen before or since. But with that progress came war, and eventually, weapons that could end those wars with little more than the touch of a button.
The world entered an uneasy truce, that no two sides with these weapons would fight each other, lest either be convinced to use them, and this this truce lasted for nearly a century.
But something had to be done. And eventually, three young scholars developed a solution.
They created a machine that could wall cities off from time, allowing flawless interdiction of the great weapons. But this great defence had a great cost, as communications that had once taken seconds now took hours, and if the target was similarly walled, months. Gone were the days where one could carry conversations across the world.
But the great weapons were once again being deployed, frequently and without warning, and so the loss was considered acceptable, and so the great age of progress ended.
That was more than two hundred years ago, by our reckoning, but outside it has been a fraction of that.
And you, brave souls, are those who would travel outside, becoming our messengers, our repairmen, our couriers, our soldiers.
Admit it, you'd read the series.