What is the threat of internal validity that occurs when external events or conditions affect one group more than another?

Question

Quizplus · Accepted Answer

The threat of internal validity known as "History" refers to events or conditions outside the experiment that may affect the participants' performance or behavior, impacting one group more than another. This can compromise the ability to attribute changes in the outcome directly to the experimental manipulation rather than these external influences.

What Is the Threat of Internal Validity That Occurs When