remove_filter('the_content', 'wpautop');

Before WordPress displays a post's content, the content gets passed
through multiple filters to ensure that it safely appears how you
enter it within the editor.

One of these filters is wpautop, which replaces double line breaks
with <p> tags, and single line breaks with <br /> tags. However, this
filter sometimes causes issues when you are inputting a lot of HTML
markup in the post editor.

This plugin displays a checkbox in the publish meta box of the post
edit screen that disables the wpautop filter for that post.

Also adds a 'wpautop', or 'no-wpautop' class to the post_class filter
to help with CSS styling.

echo nl2br(the_content);