This chart is from the Pew Research Center. They asked 1,003 people in the United States what was important to make a person an "American". The survey was done between April 4th and 24th of 2016, and has a margin of error of 3.4 points.
The quality deemed most important was the ability to speak English. That was considered at least somewhat important by 92%, and very important by 70%. About 84% said sharing American customs and traditions was important (with 45% saying it was very important).
Finishing far behind were being born in the U.S. and being a christian. About 55% said it was important to be born in this country, but only 32% said it was very important. And while 51% said being a christian was important, only 32% said it was very important. About 44% said it was not important to be born in the U.S. and 48% said it was not important to be a christian.
The charts below show the results of the same questions in Europe, Canada, and Australia.
