London is the capital city of England and has been the general hub of English politics for centuries. In the 18th century, London was known to be the center of the growing British Empire, particularly as the city that contains the legislature in Parliament and the royal family in Buckingham Palace. London saw a lot of economic growth in the 1700s with the rise of the Industrial Revolution, and as a result, the population of the city also greatly increased (Wikipedia). With these changes, however, came England's development into a stereotypical industrial city, with large crowds, low-quality sanitation, and poor living conditions (British Library).

London is mentioned twice in "A Modest Proposal," both times to describe the homeland of people who are meant to be experts or distinguished authority figures. 

"I have been assured by a very knowing American of my acquaintance in London, that a young healthy Child, well nursed, is, at a Year old, a most delicious, nourishing, and wholesome Food" (Swift)

"he confessed, that this Expedient was put into his Head by the famous Salmanaasor, a Native of the Island Formosa, who came from thence to London, above twenty Years ago, and in Conversation told my Friend, that in his Country, when any young Person happened to be put to Death, the Executioner sold the Carcase to Persons of Quality, as a prime Dainty" (Swift)

https://en.wikipedia.org/wiki/18th-century_London

https://www.bl.uk/restoration-18th-century-literature/articles/the-rise-...