I read this on Wiki... What does it mean? I already chose to give up Riften now it's asking for more. Should I say the empire shouldn't give any more territory or do I surrender Falkreath too? My games on pause as I type this =P

PS3 You can miss an Achievement/Trophy from the http://elderscrolls.wikia.com/wiki/Civil_War Quests because of how Season Unending plays out. If the faction you favor gains one or both of the forts you need, the game will not credit you, thus never giving you the Achievement/Trophy. Either ensure the opposing faction gets both Forts, or complete that portion of the Civil War Quests before you start Season Unending.