NPC stands for non player character. You can recruit them if you have the money.
Not all NPC's can be recruited. In v1.09n, when the NPC's are stacked, often it is only the leader that is recruitable. The others are tagged as Champions. The Champs are not recruitable, and once thier leader has been recuited, they can attack and be attacked by the players.
City Spam should always be a strategy but it shouldn't be the dominant one.
Right now, there's just too much advantage to having multiple production centers. We're working on this balance.
I'm glad to read that. I enjoy empire building. It is a major reason I play 4x TBS. I would not want to see empire building taken away. Balancing against the ICS strat isn't easy, but it is well worth the work! Thanks for taking the balance approach vs castration.