This page contains databases of the GDP by country from 3000BC to today. All data is normalized to total a 1,000 for the entire world in each year. The first section works mostly within the boundaries of today's states (usually), while the second section uses contemporary state boundaries.
The GDP data primarily comes from the work of Angus Maddison, with many acts of interpolation and extrapolation. Also used is PPP data from the IMF. Colin McEvedy's Atlas of World Population History, has been used to extrapolate and interpolate for the years 400BCE to 1500CE. (Maddison's first 3 data points are 1CE, 1000CE & 1500CE).
GDP by State is created with a database that indicates what proportion of today's states (the basis of Maddison's figures) was controlled at any given time. That database has been created from a variety of sources.
John Haywood, The New Atlas of World History, ISBN 9780691152691. The only source showing the entire world on a consistent map. In addition, it has a coding system for cultural development, which I used to extrapolate GDP figures before the 400BC cutoff of the Atlas of World Population History. This has been my primary source on areas outside of Europe.
McEvedy & Jones, Atlas of World Population History, ISBN 978-0140510768 though published in 1978 is still the best source. For pre-industrial cultures per Capita GDP's rarely rise far above subsistence, so population can be used as a proxy for GDP. However, later research shows that the New World was more heavily population before 1492, and I have made some adjustments.
McEvedy & Woodcock, New Penguin Atlas of Ancient History, ISBN 978-014051348
McEvedy, New Penguin Atlas of Medieval History, ISBN 978-014051249
Best source for boundaries in Europe and the Middle East. After 1000AD, I used instead
Centennia Software, Centennia Historical Atlas
Extremely detailed atlas on CD, covering, Europe, North Africa and the Middle East. The city list was used determine the proportion of each Maddison-defined country controlled by each polity
Hermann, Historical Atlas of China
Still the best source I could get of hold for detailed maps of Chinese history
West Point Atlas of Military History (website, they keep changing the url)
A good source for the complex events in China during the years of the Republic
GeaCron http://geacron.com/home-en/?&sid=GeaCron750247
This website gives political maps of the entire world from 3000BCE to today by year. Lacks the detail of Centennia, but gives more details than the books
GDP by Century 3000BCE to 2000CE