People who lived in new york city during the 9/11 terrorist attack on the world trade center experienced shared challenges due to the fact that they all experienced the attack. these challenges are an example of effects.

these challenges are an example of Cohort effects.

Cohort effects refers to a group of people that have a similar view toward the world because they shared the same experience.
The event make most of the people during that time realized the importance of taking care the national security, which lead to the formation of TSA.

Countries of eastern europe.