Answer:
The correct answer is - the phenomenon of self-fulfilling prophecy.
Step-by-step explanation:
Self-fulfilling prophecy is socio-psychological phenomenon during which an individual or a group of individuals shares a belief that a certain outcome is going to take place and this outcome takes place because their behavior and decisions align for this believe to come true.
Here, religious groups in America are aware of the idea that there is a high competition among them. Worrying that they are going to lose followers, they start to compete for new followers (behavior alignment) in order to keep the overall number of their followers.
The other good example of a self-fulfilling prophecy is bitcoin bull runs. During the latest bull run of 2019, bitcoin price went up because certain amount of people shared rumors and expectation that it will.