This whole idea of mixing spirits with juice had been introduced prior to Thomas’s time by the British in the 1700s when they came up with the idea of punch. From 1731-1766, James Ashley ran the famous Punch House on Ludgate Hill in London. It is during this time that Ashley refined the idea of punch by serving it in individual portions (cocktails?).
To this day it still remains unclear as to who was solely responsible for the world’s first cocktail. However, this excerpt from an article in the Atlantic magazine sums it up: “cocktails may have been invented in Britain, but they were roundly re-imagined and reinvented in the United States”.