1)We know VERY little about Pre War America,The only sources we have are terminals,god knows how old ghouls,and Mr.House,all who are...little less forthcoming with information
2) We dont know about the other countries,what happened to them when the atomic fire engulfed the earth? did they have vaults?
I figure this
Your a US citizen,the year is 2077,the month is September,the Day is the 1st.As the War in Alaska is ongoing,rumors you hear say there will be a nuclear exchange.You are in shock,there is a vault nearby,but you dont think you can afford it,and what about your family? can they get in too? But what if i want to join the Army,I might get shipped to China,or worse,Alaska. Soon,its October 22nd.Its almost halloween,you go to check your mail,and there it,youve been accepted into vault (insert number here) your overjoyed,as you go to tell your wife,A man in a military uniform comes up to you,soon you realise hes here to draft you,as you ponder excuses,you say your with the government,and he goes to the next house.Now the rest,is up to you.