By is used in the passive to show who or what is doing the action. Active::The cat sits on the mat Passive: The mat is sat on by the cat All the world dreaded the man with great power The man with great power was dreaded by all the world Night follows day Day is followed by night.

The word "by" has many meanings and functions. One of its functions is to show who оr what does something, in a sentence in the passive mode (страдалельный залог). It functions similarly to the Russian instrumental case (творительный падеж). For example: It was done BY HIM. (Это было сделано ИМ.) Therefore, "dreaded by all the world" tells you WHO dreaded him --- "the entire world dreadеd him" Your other example, "followed by", is of the same type. "He was followed by the police." The word "by" introduces WHO (the police) followed him. "Spring was followed by summer." The word "by" introduces WHAT (summer) followed spring. Adding the word "means" is not correct.

X is dreaded by Y means that Y is afraid of X. X is followed by Y means that Y follows, or comes after, X.

Whether it's by all the world or by all means or by means unknown, "by" is still being used in all examples to explain/point to, that which is dreading, etc.