Let's say I have a document for which all sections and subsections are separate .tex-files. As I cannot nest \include, I'm using \input.
\documentclass[a4paper,11pt,titlepage]{article}
\title{...}
\author{...}
%%Packages
\usepackage[utf8]{inputenc}
\usepackage{hyperref}
\usepackage{float}
\usepackage{caption}
%%Commands
%http://tex.stackexchange.com/questions/59245/how-to-disable-automatic-indent
\newlength\inLength
\setlength{\inLength}{\parindent}
\setlength{\parindent}{0pt}
\renewcommand{\indent}{\hspace*{\inLength}}
\begin{document}
\maketitle
\pagestyle{headings}
\input{section_A}
...
\bibliography{...}
\bibliographystyle{plain}
\end{document}
Where e.g. section_A.tex looks like this:
\section{A}
Some general blather about A and such.
\input{sub_A1}
...
And subsection-files do not contain any further inputs. E.g:
\subsection{A1}
Blah blah and so on.
\subsubsection*{A1_1}
...
\subsubsection*{A1_2}
...
If I parse that, the sub-sections will start on new pages. How can I prevent that from happening?

\inputnor\subsectioncauses a page break with the default definitions, so you need to give some hint about the code you are using. – David Carlisle Jun 10 '15 at 09:26sub_A1.texbut notsub_A2.texso we can not run the example. – David Carlisle Jun 10 '15 at 09:40\indent????? redefining a Tex primitive is very brave! – David Carlisle Jun 10 '15 at 09:41\input{section_B}and\input{sub_A2}and you should be getting a linebreak afterSome general blather about A and such.. As for redefining\indent, that was the accepted answer in the question linked to in the comment. – User1291 Jun 10 '15 at 09:49\itemand everytabbingenvironment for example (both of which use\indentinternally) – David Carlisle Jun 10 '15 at 09:52