It is my understanding that German has three passive past tenses and (I'm not sure about this) English has only two: Imperfekt: Der Euro wurde eingeführt. The Euro was introduced. Perfekt: ...
Just wondering if nachdem is the only preposition which induces a change in the tenses: Nachdem wir gegessen hatten, bin ich nach Hause gefahren. As far as I know, here it wouldn't be correct to ...