Aligning nested cases vertically

You can use \smash[t].

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[\text{Productive forces}\begin{cases}
\text{Means of production}
\smash[t]{\begin{cases}
\text{Instruments of production}\\
\text{Raw materials} \\
\text{Spaces}
\end{cases}} \\
\text{Labour power} 
\end{cases}                  
\]
\end{document}

You should consider that there might be possible surrounding text. The following puts the structure in a 4-row tabular:

\documentclass{article}

\usepackage{amsmath}

\begin{document}

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Quisque metus magna, 
placerat laoreet feugiat a, fermentum id elit. Pellentesque sodales mauris eget 
condimentum ullamcorper. Phasellus sit amet tempus nunc.
\[
  % Vertical structure containing 4 rows of items
  \vphantom{\left\{\begin{tabular}{l}
    \strut \\ \strut \\ \strut \\ \strut
  \end{tabular}\right.}
  \smash{\begin{tabular}{l}
    \strut \\ \strut \\ % Two empty rows
    \strut \smash{Productive forces
      $\left\{
      \begin{tabular}{@{} l}
        \strut \smash{Means of production
        $\left\{\begin{tabular}{@{} l}
          Instruments of production \\
          Raw materials             \\
          Spaces
        \end{tabular}\right.$} \\ \\
        Labour power
      \end{tabular}
      \right.$} \\
    \strut % One empty row
  \end{tabular}}
\]
Sed consequat, mi sed vestibulum molestie, risus orci pulvinar libero, vitae 
consequat sapien nulla vel ipsum. Nulla porta tellus arcu, ac facilisis sapien 
rhoncus et.

\end{document}

You can \smash the second cases to hide its height and add a small length accordingly, say 2\normalbaselineskip.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[\text{Productive forces}\begin{cases}
\text{Means of production}
\smash{\begin{cases}
\text{Instruments of production}\\
\text{Raw materials} \\
\text{Spaces}
\end{cases}} \\[2\normalbaselineskip]
\text{Labour power} 
\end{cases}                  
\]
\end{document}