I’m a UK author, not an American one. I have a UK publisher. That means I write in British-English. If you’re an American author, or have an American publisher – you’ll write in American-English. The two actually have more differences than you would expect.
Spelling – British English Vs American English
British words that contain -our- (colour, flavour, favourite and humour) are shortened –or- in American English (color, flavor, favorite & humor)
British words that end in –re (litre, centre, centimetre, theatre) end in –er in American English (liter, centre, centimeter, theater)
British words that end in –ise or –yse (minimise, realise, analyse) end in –ize or –yze in American English (minimize, realize, analyze)
British words that end in –ence (pretence, defence) end in –ense in American English (pretense, defense)
color – colour
fulfill – fulfil
center – centre
analyze – analyse
aging – ageing
dialog – dialogue
anesthesia – anaesthesia
Why is this?
In the early 18th century, English spelling was not standardized. Differences became noticeable after the publishing of influential dictionaries. Today’s British English spellings mostly follow Johnson’s A Dictionary of the English Language (1755), while many American English spellings follow Webster’s An American Dictionary of the English Language (“ADEL”, “Webster’s Dictionary”, 1828).
Webster was a proponent of English spelling reform for reasons both philological and nationalistic. In A Companion to the American Revolution (2008), John Algeo notes: “It is often assumed that characteristically American spellings were invented by Noah Webster. He was very influential in popularizing certain spellings in America, but he did not originate them. Rather […] he chose already existing options such as center, color and check on such grounds as simplicity, analogy or etymology”. William Shakespeare’s first folios, for example, used spellings like center and color as much as centre and colour. Webster did attempt to introduce some reformed spellings, as did the Simplified Spelling Board in the early 20th century, but most were not adopted. In Britain, the influence of those who preferred the Norman (or Anglo-French) spellings of words proved to be decisive. Later spelling adjustments in the United Kingdom had little effect on today’s American spellings and vice versa.
For the most part, the spelling systems of most Commonwealth countries and Ireland closely resemble the British system. In Canada, the spelling system can be said to follow both British and American forms, and Canadians are somewhat more tolerant of foreign spellings when compared with other English-speaking nationalities. Australian spelling has also strayed slightly from British spelling, with some American spellings incorporated as standard. New Zealand spelling is almost identical to British spelling, except in the word fiord (instead of fjord). There is also an increasing use of macrons in words that originated in Māori and an unambiguous preference for -ise endings.
Latin or French?
Most words ending in an unstressed -our in British English (e.g., colour, flavour, behaviour, harbour, honour, humour, labour, neighbour, rumour, splendour) end in -or in American English (color, flavor, behavior, harbor, honor, humor, labor, neighbor, rumor, splendor). Wherever the vowel is unreduced in pronunciation, e.g., contour, velour, paramour and troubadour the spelling is the same everywhere.
Most words of this kind came from Latin, where the ending was spelled -or. They were first adopted into English from early Old French, and the ending was spelled -or or -ur. After the Norman conquest of England, the ending became -our to match the Old French spelling. The -our ending was not only used in new English borrowings, but was also applied to the earlier borrowings that had used -or. However, -or was still sometimes found, and the first three folios of Shakespeare’s plays used both spellings before they were standardised to -our in the Fourth Folio of 1685. After the Renaissance, new borrowings from Latin were taken up with their original -or ending and many words once ending in -our (for example, chancellour and governour) went back to -or. Many words of the -our/or group do not have a Latin counterpart; for example, armo(u)r, behavio(u)r, harbo(u)r, neighbo(u)r; also arbo(u)r, meaning “shelter”, though senses “tree” and “tool” are always arbor, a false cognate of the other word. Some 16th- and early 17th-century British scholars indeed insisted that -or be used for words from Latin (e.g., color) and -our for French loans; but in many cases the etymology was not clear, and therefore some scholars advocated -or only and others -our only.
Webster’s 1828 dictionary had only -or and is given much of the credit for the adoption of this form in the United States. By contrast, Johnson’s 1755 dictionary used -our for all words still so spelled in Britain (like colour), but also for words where the u has since been dropped: ambassadour, emperour, governour, perturbatour, inferiour, superiour; errour, horrour, mirrour, tenour, terrour, tremour. Johnson, unlike Webster, was not an advocate of spelling reform, but chose the spelling best derived, as he saw it, from among the variations in his sources. He preferred French over Latin spellings because, as he put it, “the French generally supplied us”. English speakers who moved to America took these preferences with them, and H. L. Mencken notes that “honor appears in the 1776 Declaration of Independence, but it seems to have got there rather by accident than by design. In Jefferson’s original draft it is spelled honour.” In Britain, examples of color, flavor, behavior, harbor, and neighbor barely appear in Old Bailey court records from the 17th and 18th centuries, whereas there are thousands of examples of their -our counterparts. One notable exception is honor. Honor and honour were equally frequent in Britain until the 17th century; honor still is, in the UK, the usual spelling as a person’s name and appears in Honor Oak, a district of London.
Article from WIKIPEDIA.
Also sourced from: http://www.diffen.com/difference/American_English_vs_British_English