I spent a year and a half writing an economic history book that I knew was unlikely to be profitable. Nevertheless, it was a very enjoyable experience and I learned quite a bit.

https://www.amazon.com/Tyranny-Nations-Shaped-Todays-Economy...

I spent much of the past two years writing an economic history book that compares the modern United States to Victorian Britain and the Dutch Republic. Of course, Ray Dalio had to write a book on the same topic, in the same year (albeit with differing premises and conclusion). Check my book out if you're interested:

https://www.amazon.com/Tyranny-Nations-Shaped-Todays-Economy...