The English language was introduced to the Americas by the arrival of the English, beginning in the late 16th century. The language also spread to numerous other parts of the world as a result of British trade and settlement and the spread of the former British Empire, which, by 1921, included 470–570 million people, about a quarter of the world's population. In England, Wales, Ireland and especially parts of Scotland there are differing varieties of the English language, so the term 'British English' is an oversimplification. Likewise, spoken American English varies widely across the country. 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 integrating these differences came from Noah Webster, who wrote the first American dictionary (published 1828) with the intention of unifying the disparate dialects across the United States and codifying North American vocabulary which was not present in British dictionaries.