[quote=original]The year is 1463, war has ravaged all of Doman, since 1291.[/quote]
[url=https://en.wikipedia.org/wiki/Comma_splice]Comma splicing[/url]. When in doubt use a period or a semi-colon. You're writing run-ons. It's better to be a bit short and choppy than to combine clauses like that.

[quote=corrected]The year is 1463. War has ravaged all of Doman since 1291.[/quote]
[quote=alternative]The year is 1463. Since 1291 war has ravaged all of Doman.[/quote]
[quote=also acceptable]The year is 1463; since 1291, war has ravaged all of Doman.[/quote]