On the one side, the USA is just one country. Logic says it should be, then, singular, just like the United Kingdom is. Example:
The USA owns this domain.
On the other side, if I however expand "the USA" to "the United States of America", I'd tend towards using plural — the noun the verb agrees with, "States," is definitely plural. Example:
The United States of America own this domain. → The USA own this domain.
What form should I prefer?