US and U.S. are both abbreviations of United States. Both of these abbreviations can be correct. The difference between them (whether to use periods or not) is just a matter of style. The Associated Press Stylebook prefers the abbreviation U.S. with periods.

Is it better to write us or us?

In its publications, the MLA uses the abbreviation US. (Practices among publishers vary, however, and it is not incorrect to use U.S. Whichever abbreviation you choose, be consistent.) The MLA prefers to spell out the name United States in the main text of a work, in both adjective and noun forms.

Does US have two periods?

You will see examples of this abbreviation written both ways, with periods (U.S.), and without (US). ... In formal writing, spell out the two words as “United States,” as in the example below. This is always appropriate.