The united states worries that if one country becomes communist then

The United States worried that if a country became communist or had a communist takeover, there would quickly be more countries that would fall to communism, like dominos. That's why this idea is called the Domino Theory. It was mainly a Cold War policy, and was the reason the U.S. got involved with Vietnam.

The Domino Theory was and still is popular, but if your question is asking about a more recent policy, please let me know and ill find some more information for you.

explanation:

a trial judge has broad powers in his courtroom. the judge's decision is usually final for the duration of the trial, and the party's one special type of witness is an expert witness.