Split view automatic; I do not want it

It seems a recent OS update must have made the split view the default. If I am reading email and press on a link to a website, it always moves to the split view and I really do not like this, vs. switching to the Safari app for the website. And, once it is there I have trouble going back to the single app. This is frustrating and annoying. How can I control this to use or not-to-use the split view?