Table of the 3 Plagues
The First Plague
This was the first recorded plague epidemic named after the Eastern Roman Emperor Justinian at that time. Most of the port cities of the Mediterranean Sea were affected, especially Constantinople. Possibly 25% of the Eastern Mediterranean population died. This was basically most of the known world at that time. The initial outbreak killed 25 million people, and later, other outbreaks occurred until the 8th century and may have increased the death toll to 50 million. After 750, the plague disappeared until the second plague. Therefore, no living people had any immunity when the second plague pandemic hit.
The Second Plague
This was the biggest wave of the plague named the Black Death. It came from Asia over on trade boats and spread to the port cities of Europe. It quickly spread to all of Europe, infecting most countries. It ended up killing up to 60% of Europe's population and caused many problems. The second plague lasted from about 1334-1353 and left a huge mark on the world when it finally went away.
The Third Plague
This was multiple smaller outbreaks over 100 years, and usually travelled from the various world ports. This allowed the plague to become entrenched (endemic) throughout much of the world today.