- phonetic spelling change from -re to -er in words such as fibre, centre, theatre in U.S. began late 18c.; under urging of Noah Webster (1804 edition of his speller, and especially the 1806 dictionary), it was established over the next 25 years. The -re spelling, like -our, however, had the authority of Johnson's dictionary behind it and remained in Britain, where it came to be a point of national pride, contra the Yankees.
Despite Webster's efforts, -re was retained in words with -c- or -g- (e.g. ogre, acre, the latter of which Webster insisted to the end of his days ought to be aker, and it was so printed in editions of the dictionary during his lifetime). The -re spelling generally is more justified by conservative etymology, based on French antecedents. It is met today in the U.S. only in Theatre in the proper names of entertainment showplaces, where it is perhaps felt to coax a perception of high class.