Name one power that is only for the federal government.

What does this answer mean?

Some powers belong only to the federal government, and you only need to name one. USCIS accepts six: print paper money, mint coins, declare war, create an army, make treaties, or set foreign policy.

These powers come from the Constitution. Article I, Section 8 gives Congress the power to coin money, declare war, and raise and support armies. Article II gives the president the power to make treaties, with the Senate's approval, and to deal with other countries. Article I, Section 10 then forbids the states from doing many of the same things: no state can make a treaty, coin money, or issue its own paper money, and a state can't keep troops or go to war unless it's invaded or in immediate danger.

The idea is that the country needs to speak with one voice to other nations and use one currency. Splitting powers between the national government and the states is called federalism, and the next question asks about the powers that belong to the states.

At the interview, a short answer is "declare war."