Comically enough, I was really annoyed when tkinter windows opened in the background on Mac. However, now I am on Linux, and I want tkinter to open in background.
I don't know how to do this, and when I google how to do it, all I can find are a lot of angry Mac users who can't get tkinter to open in the foreground.
I should note that I am using python2.7 and thus Tkinter not tkinter (very confusing).
I am using Linux Mint. In order to make a program not show up in the foreground (i.e. be hidden behind all of the other windows), one should use root.lower() as aforementioned in the comments. However, please note (and this seems to happen on multiple platforms) that root.lower() will not change the focus of the window. Therefore, even if you use .lower() and run the script, and if you press [alt] + [F4], for example, the Tkinter window that was just opened (even though you cannot see it) will be closed.
I noticed, however, that it is prudent to place the root.lower() after attributes for the Tkinter root. For example, if you use root.attributes("-zoomed", True) to expand the window, be sure to place root.lower() after the root.attributes(..). Moreover, it did not work for me when I put root.lower() before root.attributes(..).
Start Tkinter in background