Why was eradicating smallpox a worldwide effort? what other diseases have been controlled?

Eradicating smallpox was successful because of many reasons.

Explanation:

Smallpox was regularly found in an area or we can say it was prevalent in some places. So, mortality rates were high. It was caused by variola virus and affected mainly humans. So, it was essential that such vaccine is developed which can successfully immune people from this disease.  

Smallpox vaccine then started spreading across "Europe and North America" and then gradually it spread all over the world and successfully eradicated smallpox by 1980. Other diseases that have been controlled by vaccines are “diphtheria, bacterial influenza, measles, mumps, rubella, and tetanus”.

faulty parallelism is a construction in which two or more parts of a sentence are equivalent in meaning but not grammatically similar in form.

the correct version of this faulty parallelism in the sentence is:

the hikers knew that the hike was six miles, that it usually required the entire day, and it would not be wise to start after 10: 00 a.m.

the problem is the last sentence, the first two have a basic subject+verb+object structure.

so, to give a proper balance to the structure, or better said, to give a parallel structure, we must write a basic s+v+o structure in all three sentences:

the hikers knew that the hike was six miles, that it usually required the entire day, and it would not be wise to start after 10: 00 a.m.

answer: do

the 'italicized phrase' is a noun clause that is used as a direct object.