The dates may be rather arbitrary, but the main distinction between Early Modern and Late Modern English (or just Modern English as it is sometimes referred to) lies in its vocabulary - pronunciation, grammar and spelling remained largely unchanged. Late Modern English accumulated many more words as a result of two main historical factors: the Industrial Revolution, which necessitated new words for things and ideas that had not previously existed; and the rise of the British Empire, during which time English adopted many foreign words and made them its own. No single one of the socio-cultural developments of the 19th Century could have established English as a world language, but together they did just that.
Most of the innovations of the Industrial Revolution of the late 18th and early 19th Century were of British origin, including the harnessing of steam to drive heavy machinery, the development of new materials, techniques and equipment in a range of manufacturing industries, and the emergence of new means of transportation (e.g. steamships, railways). At least half of the influential scientific and technological output between 1750 and 1900 was written in English. Another English speaking country, the USA, continued the English language dominance of new technology and innovation with inventions like electricity, the telegraph, the telephone, the phonograph, the sewing machine, the computer, etc.