The second millennium of the Anno Domini or Common Era was a millennium spanning the years 1001 to 2000. It began on January 1, 1001 (MI) and ended on December 31, 2000 (MM), (11th to 20th centuries; in astronomy: JD 2086667.5 – 2451909.5[1]).
It encompassed the High and Late Middle Ages of the Old World, the Islamic Golden Age and the period of Renaissance, followed by the early modern period, characterized by the European wars of religion, the Age of Enlightenment, the Age of Discovery and the colonial period. Its final two centuries coincide with modern history, characterized by industrialization, the rise of nation states, the rapid development of science, widespread education, and universal health care and vaccinations in the developed world. The 20th century saw increasing globalization, most notably the two World Wars and the subsequent formation of the United Nations. 20th-century technology includes powered flight, television and semiconductor technology, including integrated circuits. The term "Great Divergence" was coined to refer the unprecedented cultural and political ascent of the Western world in the second half of the millennium, emerging by the 18th century as the most powerful and wealthy world civilization, having eclipsed Qing China, the Islamic world and India. This allowed the colonization by European countries of much of the world during this millennium, including the Americas, Africa, Oceania, and South and Southeast Asia.
World population grew without precedent over the millennium, from about 310 million in 1000 to about 6 billion in 2000. The population growth rate increased dramatically during this time; world population approximately doubled to 600 million by 1700, and doubled more than three more times by 2000, ultimately reaching about 1.8% per year in the second half of the 20th century.
The Julian calendar was used in Europe at the beginning of the millennium, and all countries that once used the Julian calendar had adopted the Gregorian calendar by the end of it. For this reason, the end date of the 2nd millennium is usually calculated based on the Gregorian calendar, while the beginning date is based on the Julian calendar (or occasionally the proleptic Gregorian calendar).
In the late 1990s, there was a dispute as to whether the millennium should be taken to end on December 31, 1999, or December 31, 2000.Stephen Jay Gould at the time argued there is no objective way of deciding this question.[4] Associated Press reported that the third millennium began on 1 January 2001, but also reported that celebrations in the US were generally more subdued at the beginning of 2001, compared to the beginning of 2000.[5]Many public celebrations for the end of the second millennium were held on December 31, 1999 – January 1, 2000[6]—with a few people marking the end of the millennium a year later.