The latest version of the Varieties of Democracy (V-Dem) data, version 8, has historical data back to 1789, in addition to updated data for 2017. The full dataset is massive, but at the top level there are a handful of index variables capturing various facets of “democraci-ness”. The chart below shows the polyarchy index for all countries from 1789 to 2017. Click to zoom.
You may notice a clump of new countries in 1900. The V-Dem data use their own criteria for what states are coded in what point in time, and it does not quite match either the Correlates of War (COW) nor the Gleditsch and Ward (G&W) lists of independent states. The countries that pop up in the year 1900 with low values on the polyarchy index appear to mostly, if not entirely, be states that were at that time colonial dependencies. For example Algeria, Kenya, and Papua New Guinea. These are not in the COW and G&W lists until they gain independence in the 1950s and 1960s.