Question

What did hamilton fear would happen if the proposed constitutuion was not adopted?

Answer 1

Alexander Hamilton feared that if the proposed Constitution was not adopted then the United States would not be able to pay back its war debt, since it wouldn't have the ability to raise enough tax revenues from the sates. 

Answer 2

I believe the answer is: United States would not be able to pay back its war debt,

At that time, united states does not have the ability to raise enough tax revenues from the sates since the constitution does not explicitely granted the power for the federal government to tax the states. After the new constitution, the states are required to follow the tax regulations created by the feds.