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]).
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.
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.
Stephen Jay Gould at the time argued there is no objective way of deciding this question.