With records of subjective wellbeing going back less than half a century, this column asks if we can know the impact of key past events on the happiness of our ancestors. It presents a new historical index that draws on millions of digitised books in the Google Books corpus of words using sentiment analysis. The index – which goes back to the 1776 US Declaration of Independence, 200 years earlier than any other index of happiness – makes it possible to analyse the historical drivers of happiness in France, Germany, Italy, Spain, the UK and the US.