20th century - online puzzles

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.

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 many of the world 's species and decline in the population of others; 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 (three decades longer than it was a century ago).