Alaska and Nevada don't have too much in common beyond an abundance of open space and a history of gold rushes. But the two states share another trait that's increasingly uncommon these days: Their legislatures and governors aren't all of the same party.

The recent history of state legislative elections can be summarized with one word: homogeneity. In 1992, 16 states had single-party control of their state politics. In 2013, that number was 35. And, in a not unrelated note, that shift has been strongly toward Republicans. Of those 16 states in 1992 that were single-party run, 13 were Democratically controlled. By last year, Democrats controlled 12 -- and Republicans had leapt from three to controlling 23 states.

Part of the story is that the South was still heavily Democratic even as Bill Clinton entered the White House. We created this animation, using data from Ballotpedia, to show how single-party control evolved over time. The shift in the South, as long-standing legislators were voted out and retired in favor of new (Republican) ones is clear.

In some states the transition was rapid. In 2002, Georgia had Democrats controlling the legislature and the governor's mansion. By 2005, Republicans controlled all three. In some it was slow. Alabama moved from Democratic control to Republican over the course of nine years.

But notice how the changes come in bursts. In 2011, for example, watch the animation to see red states bloom all over the map. Students of recent history won't have much trouble in figuring out why: The 2010 midterm wave that handed the House to the GOP also had benefits on the state level.

In fact, midterms are often moments when single parties seize control of state houses. Since 1992, there have been 78 times that a state has moved to single-party control. That has happened 49 times after midterm elections -- 63 percent of the time. (By contrast, it has happened only 20 times after presidential election years.)

In the 2014 midterms, though, we could more states lose single-party control than gain it. A number of close gubernatorial races are taking place in states with single-party control: Colorado, Connecticut, Florida and Michigan. The New York Times notes that only two states -- Iowa and Arkansas -- might go solely for one party (Republican in both cases). That's in part because midterm elections favor Republicans -- and most of the states that were likely to select an all-Republican legislature and governor have already done so, after two decades of trying.

Correction: We missed Alaska's switch to single-party in 2013. The post has been updated.