What gave the US and the USSR superpower status?

There are at least two different ways in which to answer this.  First, we can say that it was military might that “gave” these two countries their status as superpowers.  Second, we can ask why it was that these two countries had so much more military might than any other country did.

In one sense, the answer to this is obvious.  The US and the USSR had superpower status because they were so much stronger than any other country.  They had larger militaries than most countries.  They had more and better military technology than other countries.  Together, these things meant that they were much stronger than anyone else.

But the more interesting question is why these countries ended up being stronger than anyone else.  First, they were stronger because they were geographically larger and had more resources. The USSR was the largest country in the world.  The United States was one of the largest.  Both countries were blessed with many natural resources.  Second, both countries were less damaged by WWII than other powerful countries had been.  The factories and other infrastructure of the US had been essentially untouched by the war.  The USSR had not been so lucky, but it did have large areas behind the Ural Mountains that had been untouched.  In addition, it was able to take machinery from Germany as part of its share of reparations.  Because these two countries were so much less damaged by the war, they were more able to create strong militaries.   Finally, both of these countries were strongly motivated to become superpowers because each needed to keep up with the other.  The US and the USSR saw one another as mortal enemies.  Therefore, each country knew that it could not let the other get ahead of it in terms of military technology.  This led to an arms race in which both countries built up their arsenals far beyond what any other countries felt they needed to do.

From this, we can see that a combination of factors led these two countries to become superpowers.  They had geographic size and wealth.  They sustained less damage during the war than other major powers.  They were more motivated to become powerful.  Because each had all three factors working for them, they became superpowers.