The English language was introduced to the Americas by British colonisation, beginning in the late 16th and early 17th centuries. The language also spread to numerous other parts of the world as a result of British trade and colonisation and the spread of the former British Empire, which, by 1921, included 470–570 million people, about a quarter of the world's population. Written forms of British and American English as found in newspapers and textbooks vary little in their essential features, with only occasional noticeable differences. Over the past 400 years, the forms of the language used in the Americas—especially in the United States—and that used in the United Kingdom have diverged in a few minor ways, leading to the versions now often referred to as American English and British English. Differences between the two include pronunciation, grammar, vocabulary (lexis), spelling, punctuation, idioms, and formatting of dates and numbers. However, the differences in written and most spoken grammar structure tend to be much fewer than in other aspects of the language in terms of mutual intelligibility. A few words have completely different meanings in the two versions or are even unknown or not used in one of the versions. One particular contribution towards formalising these differences came from Noah Webster, who wrote the first American dictionary (published 1828) with the intention of showing that people in the United States spoke a different dialect from those spoken in the UK, much like a regional accent. This divergence between American English and British English has provided opportunities for humorous comment: e.g. in fiction George Bernard Shaw says that the United States and United Kingdom are "two countries divided by a common language"; and Oscar Wilde says that "We have really everything in common with America nowadays, except, of course, the language" (The Canterville Ghost, 1888). Henry Sweet incorrectly predicted in 1877 that within a century American English, Australian English and British English would be mutually unintelligible (A Handbook of Phonetics). Perhaps increased worldwide communication through radio, television, the Internet and globalisation has tended to reduce regional variation. This can lead to some variations becoming extinct (for instance the wireless being progressively superseded by the radio) or the acceptance of wide variations as "perfectly good English" everywhere. Although spoken American and British English are generally mutually intelligible, there are occasional differences which might cause embarrassment—for example, in American English a rubber is usually interpreted