Definite article in cause and effect?

The herpes virus has affected 20 million Americans. (diagnosis)

The stethoscope improved the diagnosis of heart problems. (purpose)

The cyclotron opened the field of particle physics. (results)

The smallpox vaccine has practically eradicated the disease throughout the world. (solution)

The world seems smaller because of the telephone. (invention)

My textbook says that these are the variations of cause and effect, and in these cases you need a noun phrase using "the".

1. Are they classes?

2. Do these types of statements work like a general reference?

3. Do you think they are in an abstract sense?