"[I] tried to explain: There was an uprising against Germany, but the Russians were across the river, and on the German side there were also soldiers from Hungary or Ukraine," he said. "For Americans, it was completely incomprehensible, too complicated, because they grew up in a different historical context, where everything was arranged: America is always good, the rest are the bad guys. And there are no complications
The games are set after the events of the books, so it's kinda like Geralt just resumes his day job, but there's clues and references to all the major events that happened spread throughout.
It's not really a story about a guy who kills monsters, any more than Super Mario is a story about a plumber.
Much like Mario, he just gets caught up in a conflict between kingdoms and find himself in the midst of various political plots and webs of intrigue. But when all that is over, he just goes back to his day job.