The 'decade' of the 1920s runs from January 1, 1920 to December 31, 1929.
There have been a lot of changes during/in/over the past two 'decades'.
a 'decade' of drought [=a drought that lasted 10 years]
(..) But I want you to think about the bigger picture. Because that's what we're talking about. The work you've done with him is going to be studied for decades. You've changed the face of history Dennett. No Policeman is ever going to die in the line of duty again. Because of you. Think about that! (..)2014 RoboCop