1.US is the abbreviation of United States, which is directly translated as "America". There are two United States in the world: the United States of America and the United Mexican States, but generally speaking, the word "America" refers to the United States of America. In the article, you should write about America or America/America, and pay attention to adding the word "the" to express a specific meaning. Strictly speaking, United States(US) is the most traditional and formal name in America. This title is used to represent the United States in all international institutions, including the United Nations. On formal official occasions, when national institutions need to mention the United States of America, they generally use United States, abbreviated as US.
2.USA is the most standard abbreviation of the full name of the United States of America, but interestingly, its application scope is far less extensive than that of the United States. America is the most commonly used sports event. Almost all international sports events management organizations, including the International Olympic Committee, have strict regulations, and abbreviations in various countries must use ISO standards. It is what we often see on TV, and the corresponding international three-digit Latin alphabet code is displayed under the national flag of the contestants.
For example: USA (USA)
China (China)
These three-digit codes are strictly formulated by the International Organization for Standardization (ISO), and no country or organization may change them at will. Therefore, whether it is the national football team, basketball team and other team events or individual events, the word printed on their sportswear is "USA". When American audiences watch sports events live or in front of TV, they will feel excited. They will shout "U~S~A~" in unison, similar to "Come on China".