GovTrack.us has done the yeoman's work of pulling together the electoral history of every past member of Congress (allowing us to do things like figure out the first #Millennial to arrive in Congress: Aaron Schock, a Republican from Illinois). But it also allows us to do something else: figure out the years in American history in which the most members of Congress left office, willingly or unwillingly, never to be seen again.
We won't make you wait. In the past century, no year was the last for more members of Congress than 1933.
The reason is simple. Democrats, riding Franklin D. Roosevelt's coattails, cleaned up in the House elections of 1932. Democrats gained nearly 100 seats, taking over in 1933 for the outgoing Congress. In other wave elections, the trend is similar: larger spikes comprised more of one color than the other. After presidential elections, too, some members of Congress move into Cabinet positions, which adds to the totals.
You'll notice that the years in which more people leave occur every other year, thanks to congressional elections. But you'll notice, too, that those are sometimes in the same year as the election, and sometimes not. It depends on whether the Congress was in session into the next year, handing over the reins to the new folks.
Again, this isn't everyone who lost or everyone who left in one year but who might have been reelected later -- it's everyone in each year who left Congress and never came back. So some of the more recent years could decrease over time. Take Frank Guinta (R-N.H.). He's on here as having left in 2013, but he'll be back in 2015. Things change.
If you are a throw-the-bums-out type (which most people are), 1933 was the year the dream came true.