In Terms of the U

In terms of the U.S.wars in Iraq and Afghanistan,what has made the second phase of those conflicts so difficult?

A) Although conventional operations between states were easily won,the cost of doing so made it difficult for the United States to carry out the second phase.
B) The conventional phase of the U.S.invasion was completely unsupported in both cases,creating drag on the second phase.
C) The first phase was essentially an interstate invasion,but the second phase in both cases resulted in a domestic struggle for power.
D) In both cases,the United States did not have a clear opponent in the initial phase of either conflict.