"America will never be destroyed from the outside. If we falter and lose our freedoms, it will be because we destroyed ourselves." - Abraham Lincoln.
This quote is very applicable to the current state of our government and the state of the people. The reason this quote is significant is because there is historical precedence. For example, the fall of the Roman Empire could largely be attributed to failures within the Roman Empire. As time elapsed, laziness perfused through the people like a coursing river, corruption raged through the government with the force of a great typhoon, and the Visigoths subsequently overtook the Romans like a raging fire. America's greatest threat does not reside on foreign soil. Rather, the potential downfall of America resides squarely on the shoulders of its citizens. We can pretty effectively conclude that America will not be destroyed from the outside. America has been involved in almost a countless amount of wars with seemingly every country on Earth. The U.S government has meddled with governments in one part of the world and waged war in other parts of the world, and often in multiple places at the same time. This country has spent an ungodly amount of money on defense; the United States accounts for 40% of the world's military expenditures (source: ESPN's Men In Blazers). And if our defense system somehow fails, the fact that nearly every citizen in the South owns at least one gun (possible exaggeration) will ensure our safety. It's pretty safe to say that an outside force won't lead to our downfall. .
One example of how our downfall from within is evident in the healthcare debate. On one side of the debate, there is a group of people who desire health care at a basic level (nothing is more American than that any person has the right to own a gun, but not to have basic health care in this country). On the other side of the fence, there are people who don't want the country to become a socialist wasteland (or more likely, they just don't want to pay the extra taxes that would come with providing healthcare to all).