From the Art of Intel x86 Assembly, Page 149,
The 80386 added four control registers: CR0-CR3. These registers extend the
mswregisters of the 80286 [...]
The book says earlier that,
The 80286 microprocessor adds one major programmer-visible feature to the 8086 protected mode operation. This text will not cover the 80286 protected mode of operation for a variety of reasons. First, the protected mode of the 80286 was poorly designed. Second, it is of interest only to programmers who are writing their own operating system or low-level systems programs for such operating systems. Even if you are writing software for a protected mode operating system like UNIX or OS/2, you would not use the protected mode features of the 80286. Nonetheless, it’s worthwhile to point out the extra registers and status flags present on the 80286 just in case you come across them.
Wikipedia says this about it,
Real mode also served as a more basic mode in which protected mode could be set up, solving a sort of chicken-and-egg problem. To access the extended functionality of the 286, the operating system would set up some tables in memory that controlled memory access in protected mode, set the addresses of those tables into some special registers of the processor, and then set the processor into protected mode. This enabled 24 bit addressing which allowed the processor to access 224 bytes of memory, equivalent to 16 megabytes.
I believe today CR0 puts the CPU in Protected Mode. How did the 80286 do it?