I no longer control events, events control me

The line is taken right out of the novel. Since the author didn't attribute it to anyone else, I have to conclude it was his idea.

It's a paraphrase of Greek historian Herodotus - "circumstances rule men, men do not rule circumstances". Sometimes translated as "it is well to bear in mind that events rule men, and not men events". The basic idea probably goes back to caveman days.

It's possible that the line is a deliberate reference. The passage from which the quote comes was about the risks involved in embarking on a large-scale invasion (in this case the target was Greece).

It ends with "the land will also be thine enemy; for if no one resists thy advance, as thou proceedest farther and farther, insensibly allured onwards ... thou wilt find it more and more hostile. ... Should nothing else withstand thee, yet the mere distance, becoming greater as time goes on, will at last produce a famine."

Apart from a brief but fascinating hiccup at the Battle of Thermopylae, Xerxes almost beat the Greeks, but he couldn't go the final mile. He had to pull out and was eventually murdered by his bodyguard.

It sounds like something Abe Lincoln said. I forget what year he actually said it.