NATO was formed on April 4, 1949, which means it was created C. after World War II.
World War II started in 1939 and lasted until 1945, and a couple of years later, NATO was created. NATO stands for North Atlantic Treaty Organization, and it includes America and some European states, which decided to sign an agreement after the events of WWII. The agreement stipulates that these countries won't attack each other, and that they will always defend each other in case some other country attacks them. Other than America, France and United Kingdom are permanent members of NATO, whereas others are not.