I'm confused a bit about this sentence.

United States is/has/does .......


United States are/have/do .......

And another question.

Is this question grammatically correct ?

Has Long Beach ever experienced any environmental crisis ?
The United States is/has/does. . .

You can leave out "of America," but don't leave out "The."
It's the first one. The United States of America is a country, which is considered a single entity.

Yes, the second question is grammatically correct.
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 khoff's reply was promoted to an answer.
Thank you all.