Instruction :
How to get entrance to Istanbul from US?

Response:
To travel to Istanbul, Turkey, from the US, you will need an e-visa, even for a US citizen. Turkey is not a Schengen country. To obtain the e-visa, visit https://www.evisa.gov.tr/en/, and fill out your personal information, including the expected entry date. You will then pay $50 per visa on the website. At the end of the process, it will get a download link for the e-visa pdf file, so you can print it out.