How were polio, smallpox, the bubonic plague, the pneumonic plague, ended?

Well.. Smallpox ended as a result of an aggressive world wide vaccination program. Polio is essentially gone in the U.S. due to vaccination efforts, but is still a problem worldwide. Bubonic and pneumonic plague are caused by same organism. It is still exists and causes disease. No one knows for sure how the plague in the Middle Ages ended. Possibly quarantine, better hygiene, and warmer climate.

Related Questions

What is the difference between the pneumonic plague and bubonic plague?

Lungs / lymph nodes. The plague is usually bubonic (one catches it from being bit by infected fleas or rodents, and the bacteria infects one's lymph nodes) or pneumonic (one catches it by breathing infected moisture droplets exhaled, sneezed, or coughed out by an infected person or animal, and the bacteria infects one's lungs). Read more...
Lots. The hallmark of bubonic disease is the bubo, an extremely painful infected lymph node draining the area where the infected flea fed on the person. Pneumonic plague, the only transmissible form of the infection, can occur from spread of the bubonic stage through the bloodstream or be acquired airborne from someone else with pneumonic plague. Read more...

Could there be another epidemic of the bubonic or pneumonic plague?

No, unless.... This is extremely unlikely to happen unless it was due to bioterrorism. Read more...
Very doubtful. With today's infection control knowledge and measures, as well as general lifestyle and hygiene, this is very doubtful even in a terrorist attack, and even if the bugs are genetically engineered, robin cook-style. Read more...