Long story but I now have two ITunes libraries. One on my Macbook HD and another on a secondary external drive. In preferences I have the external one set up so when connected the Mac sees it and loads stuff there. If I am not connected it sees the one in the Home folder and stuff goes there. How can I combine the two in the library in my Home folder so I can just get rid of the one on my external drive and have one Itunes Library?
— Pat Pallentino
I would just start iTunes up with the one in your Home folder. Then drag and drop all of your content (music, video) from the external iTunes folder into iTunes to add them to it -- or just drag and drop the artists and albums that you know aren't duplicates.
It gets a little more complex if you have apps, but the basic idea is to take things from the external library folders and put them in the main library folders.
So there's no trick to it -- you just have to work to bring everything into one library.