Study countries by region

countries.wls

diff[ts_] := Transpose[{
    ts["Dates"][[;; -2]],
    Differences@ts["Values"]
    }];
merge[list_] := GatherBy[
   Table[
    Splice@
     diff[l]
    , {l, list}]
   , First];
mmerge[list_] := Table[
   {First@First@g, Total@Map[Last, g]},
   {g, merge[list]}];
With[{list = {"Americas", "Europe", "Africa", "MiddleEast", "Asia", 
    "Oceania"}},
 DateListPlot[
  Table[
   mmerge@
    DeleteMissing@
     Table[
      CountryData[b, {"Population", All}]
      , {b, a}]
   , {a, Map[CountryData, list]}]
  , Joined -> False, PlotRange -> Full, AspectRatio -> 1/3, 
  ImageSize -> Full, PlotLegends -> list
  ]
 ]