Man Created the Integers - All Else is the Work of God

A mathematician named Kronecker once said, "God created the integers, all else is the work of man."  And it's hard for me to imagine how he said that.  He was obviously more advanced at mathematics than I will ever be.  But the properties and results that flow from just a few mathematical rules are just so mind-blowingly unexpected I don't see how one could have argued that they were intentionally created instead of discovered.  

It's very easy to create the concept of an integer, but no one in the world would have thought of the argument principle in complex analysis.  No one would have intentionally created the Basel problem to sum up to its result either.  These were unexpected discoveries that seemed to stem from nature itself.  

Kronecker was apparently something called a constructivist, and I believe most of mathematics has not taken this approach.