I've thought a lot about this before, and here is what I came up with for all 50 states (and DC) and why:
Washington and Oregon - Cascadia/Pacific Northwest
California and Nevada - Snug, nicely fitting border
Idaho and Utah - Mormons
Montana and Alaska - Scenic libertarians and Native Americans
Wyoming and Colorado - Square-shaped states
Arizona and New Mexico - Southwestern states with lots of Hispanics
North Dakota and South Dakota - Both Dakotas
Nebraska and Kansans - Both Plains States; came in together with the Kansas-Nebraska Act
Oklahoma and Texas - They just seem like basically the same place
Minnesota and Iowa - Stereotypically "nice"; lots of white people
Arkansas and Louisiana - Ark-La-Tex region
Wisconsin and Michigan - Upper Midwestern states; distinctive peninsular border
Illinois and Indiana - Arguably the most "Midwestern" states
Kentucky and Tennessee - Appalachian border states
Mississippi and Alabama - The heart of the Deep South; very similar state shapes that stand "back to back"
Florida and Georgia - Deep Southern states known for fruit (Florida oranges and Georgia peaches)
South Carolina and North Carolina - Both Carolinas
Virginia and West Virginia - Both Virginias
Washington D.C. and Hawaii - Both liberal "islands", Hawaii literally and DC figuratively so
Maryland and Delaware - States that used to be Southern but aren't anymore; Delaware's borders are basically defined by Maryland
Pennsylvania and Ohio - The heart of the Rust Belt
New Jersey and New York - Lots of Italian-Americans; similar state cultures
Connecticut and Rhode Island - Both sneak in right under the wing of Massachusetts
Massachusetts and Maine - Maine used to be part of Massachusetts
Vermont and New Hampshire - Rural New England states with nearly identical shapes when flipped around and turned upside-down
You'll notice that one state doesn't have a partner - Missouri. Neither entirely North or South and at the very center of America, it is in a category of its own.
Why shows that Missouri's politics is sad.....it was a bellwether to Josh Hawley running the state's views.
