I know this will probably confuse some of you (sorry), but the year is already written correctly here; although not strictly incorrect to spell out the numbers for a year (nineteen thirty-seven), it’s quite old-fashioned (yes, even for those of you who are older than I am), so my advice is to limit year numbers as words to when you want that old-fashioned feel to your writing. Otherwise, use numerals: 3184, not thirty-one eighty-four.
Change the comma after 3184 to a period (run-on sentence).
Delete the quotation marks around book. (Even if you kept them, the comma would belong inside the quotation marks.) You can italicize that word if you want, to indicate it’s effectively a foreign word to the people of the year 3184, but it isn’t necessary.
Change 3rd to third.
The year is 3184. Inside an ancient artifact, what people of the time called a book, is written a historical account of the third world war.
Use of the word historical implies that the third world war was a past event at the time the account was written. If that’s not what’s intended, and the account was written during the war, delete historical (and change a to an so it goes with account).
I don’t like the use of ancient here. Seriously, do we refer to events and culture from the early Middle Ages as ancient? Okay, some people do, but they’re wrong, and they’re probably the sort of people who think the Victorian era, the Renaissance, and the Middle Ages are “all the same thing” and covered under the catch-all term ancient times. (You should hear Grace rant about people who refer to a historical costume as a “medieval Tudor Victorian gown.” There ain’t no such animal, folks.) Use a word such as ancient in the context of the example only if you mean to suggest that, for people in the year 3184, a bit more than a thousand years is a nearly incomprehensible span, and that the era when books were written has no connection to the current culture. (Yes, even a single word can do a lot for worldbuilding, if it’s the right word.) That doesn’t seem right, though, since they still recognize the writing (how else could they read it?), so the fact that the writing is stored differently shouldn’t make it that strange.