Before the discovery of micro-organisms, people came up with many theories as to what caused diseases. The Great Plague of London of 1665 is no different. Periodic plague outbreaks had been occurring in England for centuries, and over time a number of creative theories developed.
Perhaps the most enduring belief was that the plague was divine punishment from an angry God. This theory was particularly popular among various reformist groups, such as the Puritans, who long railed against the extravagances of the Church of England. They, along with much of the country's Catholic minority, saw the disease as the hand of God taking action against a population that had strayed from the true religious path.
Others, noting how the disease spread from person to person and from place to place, thought miasmas, or foul air, carried the disease. They sought to eliminate any bad smells by burning incense and holding sweet smelling flowers and herbs to their faces.
Some people believed that the Great Plague of 1665 was the result of a particular planetary alignment. During the 17th century, many people were turning their eyes to the night sky in an attempt to better understand their place in the universe. Advances in the telescope and celestial charts that had occurred during the Scientific Revolution meant that many people were taking note of the discovery and movements of heavenly bodies. There was a belief that there was a direct connection between the heavens and events on Earth. The fact that a bright comet had recently been seen in the sky (often interpreted as a bad omen) only reinforced this belief when this plague began.
Even though people at the time did not understand the role of microbes in spreading this disease, they did understand that infected people could transmit it to healthy people; that is why England began quarantining ships from certain ports after reports of the plague had been reported on the continent. Others thought animals were spreading the disease, and city leaders ordered a cull of the city's dogs and cats. In the end, these efforts failed to keep the disease from decimating London's population.