How to rearrange a split pane in Emacs

(the text below is my opinion, it should not be taken as fact or an insult)

With Emacs you are expected to have it open 24/7 and live inside the program, almost everything you do can be done from there. You write your own extensions, use it for note-taking, organization, games, programming, shell access, file access, listening to music, web browsing. It takes weeks and weeks till you will be happy with it and then you will learn new stuff all the time. You will be annoyed when you don't have access to it and constantly change your config. You won't be able to use other peoples emacs versions easily and it won't just be installed. It uses Lisp, which is great. You can make it into anything you want it to be. (anything, at all)

With Vim, it's almost always pre-installed. It's fast. You open up a file do a quick edit and then quit. You can work with the basic setup if you are on someone else's machine. It's not quite so editable, but it's still far better than most text editors. It recognizes that most of the time you are reading/editing not typing and makes that portion faster. You don't suffer from emacs pinkie. It's not so infuriating. It's easier to learn.

Even though I use Emacs all day every day (and love it) unless you intend to spend a lot of time in the program you choose I would pick vim

It's listed in the NEWS for Emacs (C-h N):

*** display-buffer' tries to be smarter when splitting windows. The new option split-window-preferred-function' lets you specify your own function to pop up new windows. Its default value split-window-sensibly' can split a window either vertically or horizontally, whichever seems more suitable in the current configuration. You can tune the behavior of split-window-sensibly by customizing split-height-threshold' and the new option `split-width-threshold'. Both options now take the value nil to inhibit splitting in one direction. Setting split-width-threshold to nil inhibits horizontal splitting and gets you the behavior of Emacs 22 in this respect. In any case, display-buffer may now split the largest window vertically even when it is not as wide as the containing frame.

I think what you want is:

(setq split-width-threshold nil)

(but I think you're using the vertical versus horizontal splitting the opposite of what Emacs terminology is (which is counterintuitive to me as well))