This is due to three factors: The people of the United States, how their government handles its' power, and how the problems of democracy have helped the US (to a certain extent). Technically one can boil this down to circumstance and luck. .
Americans love their freedom, so much so that they have even created habits because of it. Freedom is "something one must feel and logic has no part it. It is a privilege of noble minds which God has fitted to receive it and it inspires them with a generous fervor. But to meaner souls, untouched by the sacred flame, it may well seem incomprehensible.” The union workers that strike, the parades, the many political asylum victims, and the serving under the military services, represent the feeling. The diverse population cherishes freedom, for many of them had experienced the absence of it. One thing especially important to the concept of freedom is the crucial idea of religious freedom. Religious freedom is what which gages the workings of a person. Without it, freedom seems useless, for it is the driving factor behind the creation of freedom itself. For "freedom sees religion as the companion of its struggles and triumphs.Religion is considered guardian of mores and mores are regarded as a guarantee of the laws and pledge for the maintenance of freedom itself.” This idea is clearly represented in China, in which the state has banned religion, therefore is in constant conflict with its citizens (Falun Gong, etc.). Without religiously derived customs, how can people know whether their laws are ethically correct or not? There is no base to judge from without religion. Americans also have habits because of their freedom. When was the last time people questioned the freedom of the press? Has the government ever tried to pull newspapers off for being to anti-governmental? No, they have not. They left that choice to their citizens. If the tyranny or "despotism ever came to be established in the United States it would find it even more difficult to overcome the habits that have sprung form freedom than to conquer the love of freedom itself.