'After' isn't right. 'After the Second World War' refers to a finished time period spanning perhaps a few months or a few years following the war. Here you would use a past tense, for example 'There were severe food shortages after the Second World War' In your sentence, you are referring to the whole period from 1945 up to the present day, and the only correct preposition here is 'since'. This is an unfinished period of time, and requires a present perfect form.