Building 3 new regiments of Pikemen requires 3 available Peasant workers. If you haven’t recruited more Peasants than was required in the Labor episode, you will need to do so now.
Even if you have recruited enough Peasants, you may still face a shortage if they are busy working on production orders. You can tell at a glance how many Peasants you have and how many are working: under the labor icon (hammer) in the left scroll, there are two numbers which show the available labor and the total labor. Each Peasant unit represents 1 unit of labor.
To free up working peasants, go the Production panel and decrease some production orders.
