external

It's something that comes from outside, an external source.

The idiom, hide behind a smile, means to hide painful feelings by presenting a happy external appearance.

And you make the case that it's the external stuff, the three-prong attack, like you said, Normans in the west, the Turkic steppe people in the north, and in Central Asia, the Turks in the east.

The most important thing CIA or Mossad or MI6 looks for when they make a possible new spy is somebody who seeks validation from an external source.