American colonists favoured the monthly format, while the British Empire drifted towards the European style of dd-mm-yyyy. The American format did not cause as much confusion as the date was usually written out in full. ... America stuck with mm-dd-yyyy while the rest of the world moved to a more logical format.

Why do we write Month day Year?

The year-month-day order, such as the ISO 8601 "YYYY-MM-DD" notation is popular in computer applications because it reduces the amount of code needed to resolve and compute dates. ... Weeks are generally referred to by the date of some day within that week (e.g., "the week of May 25"), rather than by a week number.

Why does the US use mm-dd-yyyy?

One of the hypotheses is that the United States borrowed the way it was written from the United Kingdom who used it before the 20th century and then later changed it to match Europe (dd-mm-yyyy). American colonists liked their original format and it's been that way ever since.