Food is one of the resources players must produce and it is essential when developing a strong civilization. Food is absolutely necessary because it is the only resource that trains villagers which gathers more food to sustain more population.
Food is produced by the farmers working in farms located at the center
of a kingdom and is added to a kingdom's storage hourly. Important factors in food production are the number and level of farmers. Both factors directly increases the rate of hourly food production.
Without food, a permanent society can not built. Every citizen - villagers, military units and spies - consumes 1 food per hour to survive. If the required food is not supplied, military units and spies start to die due to starvation until the net food flow is rebalanced. This means that the rate of food consumption must be lower than or equal to the rate of food production.
Kingdoms have a capacity for food storage
and this capacity increases as they advance in age