American Airlines have put many USA to Europe routes on sale.
For example, fly from Washington DC to Barcelona, Spain for only $424 roundtrip with American Airlines and Iberia (see image below).
Washington DC/New York/Boston/Chicago/Seattle/San Francisco/San Jose/Los Angeles/Miami/Houston, USA
Luxembourg City, Luxembourg
(same as DEPART)
Availability from January to November 2018 (excluding summer)
Complete the search box with the example dates listed above: