The US still did its best not to get its feet dirty in WWI's trenches, but finally capitulated in 1917, sending over a million troops to help sort out the pesky Germans. Postwar celebrations were cut short by Prohibition in 1920, which banned alcohol in the country. The 1929 stock-market crash signaled the start of the Great Depression and eventually brought about Franklin Roosevelt's New Deal, which sought to lift the country back to prosperity. After the Japanese dropped in uninvited on Pearl Harbor in 1941, the US played a major role in defeating the Axis powers. Atomic bombs dropped on Hiroshima and Nagasaki in 1945 not only ended the war with Japan, but ushered in the nuclear age. The end of WWII segued into the Cold War - a period of great domestic prosperity and a surface uniformity belied by paranoia and betrayal. Politicians like Senator Joe McCarthy took advantage of the climate to fan anticommunist flames, while the USSR and USA stockpiled nuclear weapons and fought wars by proxy in Korea, Africa and Southeast Asia. Tensions between the two countries reached their peak in 1962 during the Cuban Missile Crisis.

　　The 1960s was a decade of profound social change, thanks largely to the Civil Rights movement, Vietnam War protests and the discovery of sex, drugs and rock & roll. The Civil Rights movement gained momentum in 1955 with a bus boycott in Montgomery, Alabama. As a nonviolent mass protest movement, it aimed at breaking down segregation and regaining the vote for disfranchised Southern blacks. The movement peaked in 1963 with Martin Luther King Jr's 'I have a dream speech' in Washington, DC, and the passage of the landmark 1964 Civil Rights Act and 1965 Voting Rights Act. Meanwhile, America's youth were rejecting the conformity of the previous decade, growing their hair long and smoking lots of dope. 'Tune in, turn on, drop out' was the mantra of a generation who protested heavily (and not disinterestedly) against the war in Vietnam. Assassinations of prominent political leaders - John and Robert Kennedy, Malcolm X and Martin Luther King Jr - took a little gloss off the party, and the American troops mired in Vietnam took off the rest. NASA's moon landing in 1969 did little to restore national pride. In 1974 Richard Nixon became the first US president to resign from office, due to his involvement in the cover-up of the Watergate burglaries, bringing American patriotism to a new low.

The 1970s and '80s were a period of technological advancement and declining industrialism. Self image took a battering at the hands of Iranian Ayatollah Khomeni. A conservative backlash, symbolized by the election and popular two-term presidency of actor Ronald Reagan, sought to put some backbone in the country. The US then concentrated on bullying its poor neighbors in Central America and the Caribbean, meddling in the affairs of El Salvador, Nicaragua, Panama and Grenada. The collapse of the Soviet Bloc's 'Evil Empire' in 1991 left the US as the world's sole superpower, and the Gulf War in 1992 gave George Bush the opportunity to lead a coalition supposedly representing a 'new world order' into battle against Iraq. Domestic matters, such as health reform, gun ownership, drugs, racial tension, gay rights, balancing the budget, the tenacious Whitewater scandal and the Monica Lewinsky 'Fornigate' affair tended to overshadow international concerns during the Clinton administration. In a bid to kickstart its then-ailing economy, the USA signed NAFTA, a free-trade agreement with Canada and Mexico, in 1993, invaded Haiti in its role of upholder of democracy in 1994, committed thousands of troops to peacekeeping operations in Bosnia in 1995, hosted the Olympics in 1996 and enjoyed, over the past few years, the fruits of a bull market on Wall St. The 2000 presidential election made history by being the most highly contested race in the nation's history.