Quote Originally Posted by emsr2d2 View Post

The Civil Rights movement has happened. It's over. (Please don't take that as a political statement!)

The Civil Rights movement was successful. Had it not been successful, the world would be a very different place.
The Civil Rights movement was successful. If it had not been successful, the world would be a very different place.
NOT A TEACHER

I understand this represents the "the third mixed conditional". However I have to say, that I do not find it in any ordinary course of grammar. Why?