In 1783 Noah Webster in the United States produced a spelling book which proposed minor changes in the spelling of some words. The proposals were largely accepted by the American public, so that now there are some differences between the spelling of American English and the English used in other countries.
The changes included the use of -or instead of -our as in color and honor;
and the use of -er instead of -re as in theater and center. Other changes
included catalog (catalogue), gray (grey), program (programme), jail (gaol),
and leaped (leapt).