Economic productivity has declined in some countries as a result of:

As for me, I think that the main reason of the declining of economic productivity in some countries is a war.  In the conducting of military operations by the State in view of the mobilization of the whole array of the armed forces, the country's economy begins to unwittingly work on the process of the war as a whole. Often companies that previously engaged in manufacturing of any civil or technology things are changing skills and become involved in the manufacture of military items.  Also on war spending huge amount of money. Even taking into account the positive outcome of the final - winning - is not to say that the war - this is a positive factor for the economy.

during the ming dynasty

a. theta waves. this is because the person is in a light sleep which means the brain waves would show these kind of waves.