Atlanticism is a big word that means countries that are friends with each other across the Atlantic Ocean. Atlantic Ocean is a very big ocean that separates America and Europe. Atlanticism is a special relationship between those two places. It started after World War II when America and Europe made an agreement to help each other out, like best friends do. They wanted to make sure they were always there for each other, even if they were very far away. They also wanted to create a strong team by working together on things like business, science, politics, and the military.
Think of it like having a best friend who lives far away from you. You still love and care about each other, and you talk on the phone, send letters, and visit each other as much as you can. You also know that if your friend ever needs help, you will be there to support them.
So, Atlanticism is like having a best friend across the ocean that you can always count on.