Which is a power that enables the United States to engage in war?

• A. Enter war
• B. Postal
• C. Armies
• D. Federal property

Answer: (A)

The key idea here is the authority to authorize entering into hostilities. In the U.S. system, the formal power to declare war rests with Congress, and that declaration enables the nation to engage in armed conflict by mobilizing resources and military forces. While the President can lead the military as Commander-in-Chief and can act under authorization or in certain urgent situations, the official step that enables a country to enter war is Congress declaring war.

So the option that captures this mechanism is the act of declaring or entering into war. The other options don’t fit: postal has nothing to do with war powers, armies are the forces themselves rather than the power to authorize war, and federal property is unrelated to initiating hostilities.