Question

The fact that there was no national military under the Articles of Confederation was a weakness in which area of government?

Answer 1

The essentials of this line can be best found out in the chapter called "The need for a constitution". The fact that there was an absence of national military system under the articles of confederation indicate a weakness in the administrative form/area of government.

It is the duty of the government of any country to administrate over all major activities that are related the people of all the states. It there is no military power, it indicates that the administration system is inappropriate and needs to be modified for betterment of people within  a country.