Parindent not working for subsection paragraph [duplicate]

This is the code:

\section{Introduction}

\subsection{Background of the Project}
\setlength{\parindent}{10ex}
An Information System (IS) is a collection of integrated modules that collect, manipulate, and...


This is the output:

The \parindent doesn't seem to be working. I need the paragraph to be indented.

I'd prefer a global solution, where all paragraphs are indented unless otherwise instructed.

• parindent is likely already set to a useful value; you don't need to set it again. The first paragraph after a heading (like the subsection above) is not intended by default, because that is the standard typographic convention in the English world. You can use the package indentfirst to override this. See questions 1, 2, 3, 4, etc. – ShreevatsaR Sep 7 '17 at 2:43
• And welcome to TeX.SE! Good luck with your typesetting. From your next question, please include a complete (but minimal) compilable example, starting with (if you're using LaTeX) \documentclass and ending with \end{document}. – ShreevatsaR Sep 7 '17 at 2:44

LaTeX don't indent the first paragraph after of a title (section or subsection, etc). Use the package indentfirst.

\documentclass{article}
\usepackage{indentfirst}
\begin{document}
\section{Introduction}

\subsection{Background of the Project}
\setlength{\parindent}{10ex} % ???
An Information System (IS) is a collection of integrated modules that collect, manipulate, and...

Other paragraph ...
\end{document}