The United States of America is the second largest country in North America and third largest on Earth and comprised of fifty states and a federal district.
The United States was one of the main proponents in World War II, allied with the United Kingdom, the Soviet Union and France. The U.S. became entangled in the war after the attacks on Pearl Harbor (in Hawaii) by Japan's Imperial Navy, and the two countries became two of the strongest nations in the fight. The U.S. ended WWII by dropping nuclear bombs on the Japanese military cities of Hiroshima and Nagasaki, which resulted in mass destruction and many deaths.
Several years later in 1954, America was carrying out a Nuclear Test codenamed Castle Bravo. Fallout from this test at the Bikini Atoll drifted over a Japanese fishing boat called the Daigo Fukuryu Maru (Lucky Dragon No. 5), and led to its occupants suffering from radiation sickness shortly after returning to Japan. It was these two bombs, plus the later test and the resulting horror and destruction that led to the idea for Godzilla.
The United States has been attacked several times by kaiju, with Godzilla attacking New York City, New York in Destroy All Monsters, and both Honolulu, Hawaii and San Francisco, California in Legendary Pictures' Godzilla. Zilla also stormed across America and engaged the military in NYC during the events of GODZILLA. Also in the film, Cloverfield, a monster attacked New York City and caused significant destruction. And even Rodan attacked New York City in Godzilla: Final Wars.