The 21st century began with the United States as the sole superpower in the absence of the Soviet Union, with China emerging as a potential superpower. The debate over what should be done about fossil fuel pollution and alternative energy raged in the new century after most of the 20th century was marked by rapid industrial expansion. As the Cold War was over and Islamic fundamentalist-related terrorism on the rise, the United States and its allies turned their attention to the Middle East.
Digital technology – in its early stages of mainstream use in the 1980s and 1990s – became widely adopted by most of the world, though concerns about stress and anti-sociality from the overuse of mobile phones, the Internet and related technologies remained controversial. Over 1.5 billion people worldwide used the Internet by the end of the first decade and over 4 billion (more than half the world's population) used cell phones.