I’ve been looking for a disease, off and on for the last 5 years, one that could have originated in the Americas, but would have had the same effect on Europe in an Alternate History scenario as smallpox had on America as ours.And finally Tuberculosis has put its hand up shouting ‘pick me – pick me!’

To me the disease seems tailor-made for its role as a decimator of civilisations. It has been co-evolving with humanity for over 70,000 years. Despite being quite a slow growing bacteria at times in our past it has been responsible for 25% of all deaths. In addition its virulence has been closely linked to the human environment, so the larger the city the greater the virulence. More importantly there is evidence that human populations can develop a genetic based resistance to the disease.

Put it all together and all you need to create the perfect disease that decimates Europe and/or Asia, allowing for a American colonists to move in and simply takeover, is:

• the development of American cities to serve as breeding cultures
• a couple of minor mutations within the TB bacteria to increase its virulence
• enough time for the American population to have developed some genetic resistance to the disease