The Adventure Of English
Early Modern English lacked uniformity in spelling, but Samuel Johnson's dictionary, published in 1755 in England, was influential in establishing a standard form of spelling. Noah Webster did the same in America, publishing his dictionary in 1828; see American and British English spelling differences.
Public education increased literacy, and more people had access to books (and therefore to a standard language) with the spread of public libraries in the 19th century. Many words entered English from other languages as a result of contact with other cultures through trade and settlement and from the migration of large numbers of people to the United States from other countries. World War I and World War II threw together people from different backgrounds, and the greater social mobility afterwards helped to lessen the differences between social accents, at least in the UK. The development of radio broadcasting in the early 20th century familiarised the population with accents and vocabulary from outside their own localities, often for the first time, and this phenomenon continued with film and television.