The United States is a country in North America that is seen briefly, but mentioned multiple times in Neon Genesis Evangelion.
Until the end of the 20th Century the United States was the World's most powerful nation in all military, economic and diplomatic standards. The U.S. was a Permanent Member of the United Nations Security Council and a close ally of Japan. Despite the highly destructive effects of the Second Impact Event, it seems that the U.S. wasn't damaged as severely as Japan and the rest of the world. After the Impact Event the U.S. lent a significant portion of its military capacity to the United Nations to help rebuild the world and oppose the Angels. NERV also established manufacturing operations in the U.S. through its First and Second Branch.
The United States provided strong support to NERV, the Japanese Strategic Self Defense Force and the United Nations to counter the worldwide Angel threat. The United States agreed to build Eva Units 03, 04 and 06. Multiple U.S. ships of the UN Pacific Fleet were attacked and sunk by the angel Gagheil in an engagement where Unit 2 managed to kill the aquatic beast. Germany sent a repaired S2 Engine to NERV's 2nd Branch in Nevada to complete the construction of Unit 4. However, due to interference from the angel Leliel, the Unit's S2 Engine malfunctioned, causing a Dirac Sea which destroyed the entire facility within an 89 kilometer radius and killed several thousand workers. After this event the United States removed Unit-3 from its storage at NERV's First Branch in California and sent it by cargo jet to Japan. Unfortunately, Unit 3 was hijacked by the hidden angel Bardiel over the Pacific in transit.
Economy and Politics
The United States was one of the few nations with an economy large and complex enough (aside from Japan and Germany) to be capable of building an Evangelion Unit. During 2015 it seems the country was undergoing an economic crisis as evidenced by high unemployment rates. While the Country was a powerful member of the United Nations Council, the U.S. Congress was still obstinate to contribute to the funding of additional Eva Units beyond Unit 5. However, Congress was concerned about the ongoing unemployment crisis and agreed to funding on the condition Unit 6 was also built in the U.S. to create jobs for citizens. The U.S. maintained a large manufacturing sector, particularly in the aerospace division.
The United States contributed to the bulk of the United Nations' military force after the Second Impact. The UN Pacific Fleet was composed of five aircraft carriers and two battleships built before the Second Impact. The U.S. Navy had moved its Pacific Fleet Headquarters to New Yokosuka.