? When is the last time a State was split?
I'm thinking it was West Virginia. Not counting territories that were divided.
Before WV it was Maine from Massachusetts.
It's been a long time. Reorginization of political boundaries hasn't been common in recent history, aside from a new county in Colorado and some local government consolidation. The will for such major changes is lacking from our staid status quo universe. If I were dictator I'd have a top to bottom review of all levels of government, splitting up states and counties like nobodies business. ;)
During the early 1860’s, West Virginia split from Virginia. North Dakota and South Dakota split apart while still territories, and the same happened with North Carolina and South Carolina.
A North California and South California wouldn’t hurt anything at all.