Where do you assume those castles came from? My guess would be winning sieges.
Well sir, most of those castles actually came about from the voting system used in the beginning of this round of Strategus. In addition, other castles were absorbed into their group from clans that joined up with them. Some were taken by force though (most of which were given away to other folks).
Hm, most actually came out of the KUTT conquest. they only started with that central area near Sargoth.
Ismarala, Jelbegi, Sargoth, Knudarr: Vote
Tilbaut: Annex
Derchios: Captured
Kelredan: Captured, Sold
Senuzgada: Captured, Sold
Reyvadin: Captured
Ichamur: Captured
Sengutche: Captured, Sold, Absorbed(?), Independent
Yruma: Captured, Sold
Slezekh: Captured, Sold, Absorbed later
There were some others, most likely.