Every four years, the nations of the world set aside their differences for a few weeks and join in the spirit of athletic competition at the Olympics.

That's the plan, anyway.

But invariably, politics take center stage. One nation or another decides to boycott the Games over an urgent social/political issue, and the sense of unity is further shattered by a grab bag of other divisive issues, from security to air quality to the readiness of the venues.

In the case of this summer's Games in China, it's all of the above and more. Months before the opening ceremony, even something as mundane as the photo-op-heavy Olympic torch relay has turned into a show of worldwide protest instead of unity.

What are the issues?: Tibet and Darfur. Human-rights organizations have been protesting China's treatment of Tibet since the Asian superpower took the smaller country by force in 1951, sending its spiritual leader, the Dalai Lama, into exile. In their bid to host this year's Olympics, China promised to improve its human-rights record, but recent anti-China protests in Tibet turned bloody as Chinese security forces clashed with Tibetan Buddhist monks, resulting in at least 16 deaths.

In addition, China has been harshly criticized for continuing to be the largest trading partner of Sudan. Most Western oil companies have withdrawn from the African nation to protest the government, which has forced hundreds of thousands of citizens off oil-rich lands without any compensation. China buys two-thirds of Sudan's oil exports and, in exchange, sells heavy weapons to Sudan. Since 2003, the country has displaced more than 1 million people and taken the lives of more than 200,000, leading some to label it genocide. Western nations, threatening a boycott of the Games, have urged China to put pressure on the Sudanese government to cooperate with peacekeeping forces.

What's up with the torch protests?: The Olympic torch relay is usually a pregame victory lap of sorts, a feel-good event that allows hundreds of dignitaries, athletes and regular folks to get their hands on one of the Games' symbols of good will as the flame makes its way from ancient Greece to the host city. This year's 130-day, 85,000-mile torch run began on March 24 in Ancient Olympia, where protesters briefly disrupted the lighting ceremony.

On Sunday, thousands of protesters crowded London streets and more than two dozen were arrested along the torch path. Organizers had to cancel the final leg of the Paris route after chaotic protests on Monday, which included people blocking and attempting to tackle the runners, and one man's effort to snuff out the flame with a fire extinguisher. The violent clashes forced Chinese officials to douse the flame a record five times as they took it off the streets and onto buses to move it along the route.

The most dramatic protest to date, however, occurred in San Francisco on Monday, two days before the only North American leg of the relay was scheduled to take place. Three protesters climbed the cables of the Golden Gate Bridge and hung the Tibetan flag and two banners that read, "One World. One Dream. Free Tibet." and "Free Tibet," as a precursor to what is expected to be a vigorous protest presence in the city.

The flame's around-the-world trip is the longest in Olympic history and was intended to symbolize China's rising political and economic strength. Angry that human-rights issues have once again grabbed the headlines, Chinese officials have lashed out at protesters, criticizing them for attempting to disrupt the Olympic spirit and politicizing the Games.

The torch will likely face more demonstrations as it continues its global journey before arriving on the Chinese mainland on May 4. The Associated Press reported on Tuesday (April 8) that the International Olympic Committee might consider canceling the rest of the international leg of the relay during a meeting on Friday.

The torch is scheduled to travel to Buenos Aires, Argentina, next. The Olympic Games open on August 8.