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]
(..) Scotty, the last hatch won't open. - Scotty. - Work fast, Captain. Time is running out. He is not gonna make it. What would I do without you, Spock? For decades, the Federation taught that he was a hero. I guess time would judge us all. He just got lost. You saved this entire base, Kirk. (..)2016 Star Trek Beyond