Claim: David Simon was born in the twentieth century.

The 20th century was a century that began on   January 1 , 1901 and ended on December 31 , 2000 . It was the tenth and final century of the 2nd millennium . It is distinct from the century known as the 1900s which began on January 1 , 1900 , and ended on December 31 , 1999 .   The 20th century was dominated by a chain of events that heralded significant changes in world history as to redefine the era : World War I and World War II , nuclear power and space exploration , nationalism and decolonization , the Cold War and post-Cold War conflicts ; intergovernmental organizations and cultural homogenization through developments in emerging transportation and communications technology ; poverty reduction and world population growth , awareness of environmental degradation , ecological extinction ; and the birth of the Digital Revolution . It saw great advances in communication and medical technology that by the late 1980s allowed for near-instantaneous worldwide computer communication and genetic modification of life . The term `` short twentieth century '' was coined to represent the events from 1914 to 1991 .   Global total fertility rates , sea level rise and ecological collapses increased ; the resulting competition for land and dwindling resources accelerated deforestation , water depletion . and the mass extinction of half the world 's estimated nine million unique species and wildlife population ; consequences which are now being dealt with . It took all of human history up to 1804 for the world 's population to reach 1 billion ; world population reached an estimated 2 billion in 1927 ; by late 1999 , the global population reached 6 billion . Global literacy averaged 80 % ; global lifespan-averages exceeded 40 + years for the first time in history , with over half achieving 70 + years -LRB- three decades longer than it was a century ago -RRB- .