The iPhone 6s is arguably the best smartphone available at the moment, and a large part of that success is Apple's "in-house" mentality where it makes and designs its hardware and software to work with each other.
But Apple doesn't do it on its own.
It relies heavily on a bunch of different tech companies to make the parts for the iPhone, and some of them even come from competing smartphone makers like Samsung. Apple has to make sure those parts play nicely with the other important parts, as well as the iPhone's operating system, iOS.
Check out which companies make some of the iPhone's most important parts and where they're made: