The hints: Seven, three, no pig-stabbing
Rome: Seven hills of Rome, led by a triumvirate. Stabbing pigs was a greek tradition, not a roman one (so PDOX has the chance to correct the error we saw in EU:Rome).
Game of Thrones: Seven Kingdoms were united, three houses (Stark, Lannister, Arryn) became the Wardens. King Robert Baratheon dies when a pig stabs him.
China: Seven Warring states, Three Kingdoms, pigs were very valuable in China and definitively not stabbed (at some point in history stabbing a pig you didn't own was comparable to manslaughter).