The measuring system used by the United States is a slightly modified (or non-modified) version of the British Imperial system used by the British Empire until they began to utilize the metric system wherein the British imperial system was replaced by the newer metric system in British domains in tandem with other countries also beginning to adopt this system of measurement and no longer using a system unique to their own country. As the United States was not a member of the commonwealth or the British Empire, as well as a non-European nation there was very little reason for them to abandon a system that they had been using an extended period of time.

Sorry this is a bit vague, hope this helps!