From protected and armored cruisers to light cruisers

How did protected, armored, and unprotected cruisers differ, and why did those categories disappear?

They marked different protection levels, but improved light-cruiser armor and later treaty definitions made the old categories obsolete.

The hierarchy runs from unprotected cruisers through third-, second-, and first-class protected cruisers to armored cruisers. The categories represented increasing expectations of protection and combat survival rather than a simple linear change in size. By around 1910, useful armor could be fitted to light cruisers at acceptable cost, eliminating much of the case for an unprotected type. Treaty definitions then reorganized cruiser language around new displacement and gun-caliber rules, pushing the older labels out of common use.