Methodology:
This dataset reconstructs historical economic and demographic indicators (GDP (PPP) and population) based on historical political boundaries. Using the Maddison Project Database as a foundation, along with several other sources, I aggregated historial GDP and population figures. Much of the data collected was based on the modern-day borders of countries, so figures often had to be added together to arrive at the total GDP/population of a historical polity; for example, the British Empire's GDP includes the combined GDPs of the United Kingdom, Ireland, Canada, India, and many other countries. Colonies, puppet states, and military-occupied territories are all directly counted toward the GDP/population of a given country/empire. Where historical polities controlled only portions of present-day states, I estimated their share by identifying the subnational regions corresponding to the territory controlled by the polity and assigning proportional weights based on population distributions from the closest available census data including those provinces.
To address gaps in temporal and geographic coverage, I employed several estimation techniques. When country-level data were unavailable for earlier periods but regional estimates existed, I extrapolated backwards by applying each country’s earliest observed share of regional GDP or population to prior years. Additionally, missing values "in between" figures were estimated via linear interpolation between the closest data points in time. Together, these methods produce a consistent yet approximate long-run dataset that prioritizes historical territorial accuracy while maintaining comparability across time, the first long-run economic dataset to account for the territorial evolution of different countries.
By its very nature, this database has significant limitations. Most of the figures included should be treated as rough estimates, especially as the data extends further into the past. The data presented is my best attempt at reconstructing figures, in some case highly speculative, while minimizing inaccuracy. Figures from 1950 onward are compiled directly from the Maddison Project database and several population sources, then added together when necessary to account for colonial empires, so they have the highest degree of accuracy. From 1820 onward, direct estimates were available for most of the countries analyzed, but some GDP figures were missing and had to be calculated using regional proportions, especially in subsaharan Africa and smaller Asian countries. Therefore, the data from 1820-1950 is highly accurate for North America, Europe, and East Asia, but data for colonial empires and non-Western polities is less grounded. Additionally, interpolation becomes much more common before 1950. Finally, pre-1820 GDP figures are reconstructed based on information about a select group of countries (most of Western Europe, the United States, Greece, Poland, several Middle Eastern countries, China, Japan, Mexico, South Africa, Brazil & Indonesia (these two have very little pre-1820 data) ), along with estimates for other countries based on a their projected GDP proportion of their region, and is largely conjectural. Population data is more grounded than GDP data pre-1820 (and in general), as many estimates exist both for historical states and modern-day borders, but still questionable in certain cases (particularly, the Aztec and Inca Empires).
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