Yama: Buildings
Houses allow your lands to accommodate more people than barren lands. Hence more population equals more taxes and money at your disposal.
Farms are the places where you grow your own food. Without food, a portion of your population may starve to death.
Libraries are the places where you can get more research points each turn. Research points can help enhance your kingdom efficiency in various aspects without resorting to physical improvements.
Forts to some extent represents the military might of a kingdom. With more presence of Forts in your kingdom, they help increase your forces morale and therefore increase the efficiency of them during combat, both defending and attacking wise.
Barracks are the training grounds of your military forces. They help decrease military drafting time and provide your military forces with better fighting skills.
Markets represent the well being of a kingdom. They help cut costs of drafting military as well as lower the cost of buying things. Basically, they also helps buying construction materials at a lower price, hence decreasing your building costs.
Armories help your kingdom reduce costs of constructing buildings and lowers the time required to draft military units.