In order to purchase a 2nd village you would need to reach Rank 12 (Alderman), have researched Leadership 1,  and have the gold available to buy the village, along with a captain. You cannot buy a village without a captain, who is created by researching: Military, Leadership, Captains.

You can buy more villages later as your rank increases and you research further levels of Leadership.

Please see the wiki for more details: http://help.strongholdkingdoms.com/index.php/Villages