LONDON (Reuters) - As the past decades have demonstrated, the euphoria and glamour associated with staging the Olympic Games can quickly dissipate through forces often beyond the host city's control.
Beijing's successful bid in Moscow seven years ago to host the 2008 Olympics won worldwide approval after the Chinese capital had narrowly lost the 2000 Games to Sydney.
However, China's goal of portraying an image of a united, peaceful and prosperous society is now being undermined daily through a government crackdown on anti-Chinese protests in Lhasa, capital of the mainly Buddhist Himalayan region of Tibet.
This month, athletes' concerns about pollution were highlighted when world record holder Haile Gebrselassie said he would not run the marathon in Beijing because of health concerns.
Munich in 1972 and Montreal four years later were host cities which found the Games could become a poisoned chalice.
Munich had planned to showcase the political, economic and social successes of post-war Germany in the same fashion that the 1964 Tokyo Games had illustrated Japan's emergence from the devastation of World War Two.
Instead, a Games designed to celebrate peace were the venue for the so-called "Munich massacre" which changed the face of sporting events forever.
Two Israelis were initially killed and nine taken hostage after eight Palestinian guerrillas easily infiltrated the flimsy security at the Olympic village.
The Palestinians demanded the release of around 200 prisoners in Israeli jails and safe passages for themselves.
But eventually nine hostages, five of the Palestinians and a policeman were killed when German marksmen opened fire at a military airport.
The citizens of Montreal and Canada were left with a C$1.5 billion debt which took three decades to pay off after the construction budget soared out of control. Ticket sales were hit when African nations walked out in protest against a New Zealand rugby tour of racially segregated South Africa.
In 1980 the United States and many western countries refused to compete in Moscow after the Soviet invasion of Afghanistan in the previous year. To nobody's great surprise the Soviet Union and its eastern bloc allies retaliated by boycotting the 1984 Los Angeles Games, citing security concerns.
A fourth boycott of the equally politically sensitive 1988 Seoul Games could have spelled the end of the Olympic movement.
By now, though, the political climate had changed. After prolonged negotiations, North Korea failed in a audacious bid to jointly stage the Games and in the end only they Cuba, Ethiopia and Nicaragua stayed away.
In 1968, the International Olympic Committee (IOC) was criticized when it declined to take a stand after government troops shot dead around 250 demonstrators protesting against the cost of the Mexico City Games 10 days before the opening ceremony.
It was, the IOC said, "an internal affair" and none of their business.
Two weeks later, the IOC was again under an unwelcome spotlight when it urged the U.S. Olympic Committee to expel sprinters Tommie Smith and John Carlos from the Games for their silent 'salute' protest on the victory podium against the treatment at home of their fellow black Americans.
IOC president Jacques Rogge, elected to succeed Juan Antonio Samaranch at the same Moscow congress which awarded this year's Games to Beijing, has faced one demanding test of his leadership qualities.
The 2002 Salt Lake City Winter Games were in doubt after the attacks on New York and Washington on September 11, 2001. They went ahead without incident, thanks to unprecedented security costing around $310 million.