\begin{longtable}[]{@{}
  >{\centering\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.30}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.30}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.20}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.20}}@{}}
\caption{States belonging to the \emph{Nordics.}}\tabularnewline
\toprule
Name & Capital & \vtop{\hbox{\strut Population}\hbox{\strut (in 2018)}} &
\vtop{\hbox{\strut Area}\hbox{\strut (in km\textsuperscript{2})}} \\
\midrule
\endfirsthead
\toprule
Name & Capital & \vtop{\hbox{\strut Population}\hbox{\strut (in 2018)}} &
\vtop{\hbox{\strut Area}\hbox{\strut (in km\textsuperscript{2})}} \\
\midrule
\endhead
Denmark & Copenhagen & 5,809,502 & 43,094 \\
Finland & Helsinki & 5,537,364 & 338,145 \\
Iceland & Reykjavik & 343,518 & 103,000 \\
Norway & Oslo & 5,372,191 & 323,802 \\
Sweden & Stockholm & 10,313,447 & 450,295 \\
Total & & 27,376,022 & 1,258,336 \\
\bottomrule
\end{longtable}