Final answer:
Congress struggled to declare war and establish an Army/Navy because they didn't have the power to raise an army or navy, relying on the states for soldiers.
Step-by-step explanation:
Congress struggled to accomplish their goal of declaring war and establishing an Army/Navy because they lacked the power to raise an army or navy. The fear of a standing army in the hands of a tyrannical government led to the writers of the Articles of Confederation leaving defense largely to the states. Congress had to depend on the states to provide soldiers, and if the states chose not to honor the national government's request, the country would lack an adequate defense. This was dangerous at a time when England and Spain controlled significant portions of North America.