What did Eli Whitney use to show the U. S. patent office the usefulness of interchangeable parts

Interchangeable parts, popularized in America when Eli Whitney used them to assemble muskets in the first years of the 19th century, allowed relatively unskilled workers to produce large numbers of weapons quickly and at lower cost, and made repair and replacement of parts infinitely easier.

What effect did the development of trade have on settlement patterns in medieval times

The enforcement of a peace settlement