If you want to travel from Spain to the United States, the process is simple. You register online through the Electronic System for Travel Authorization (ESTA), pay a fee of $14, and either get an instant answer or wait a day or two while the U.S. government checks to make sure that you are not a terrorist or a wanted criminal. Your stay can last up to three months, no questions asked.
If you want to travel from Brazil to the United States, however, you will first need to apply for a visitor visa, pay a fee of $140, and then
Source URL: https://www.foreignaffairs.com/articles/americas/2012-04-09/if-you-extend-visa-waiver-program-they-will-come