Interest rates on sovereign debt are higher in the US. The US government is paying 2.6% to its creditors. Meanwhile, people are accepting 10 year loans for only 2.3% interest in Canada and Singapore, 2.1% in Hong Kong, 1.9% in France and Sweden, 1.5% in Germany and Taiwan, 0.9% in the Euro area, 0.8% in Switzerland, and 0.6% in Japan. (Trading Economics http://www.tradingeconomics.com/bonds) Thus, people have more faith in the governments of all these countries than they do in our government.
The debt to GDP ratio of many of these countries is worse than that in the US (at 74% of GDP), Japan 214%, Singapore 111%, France 90%, Canada has 84%, Germany 82%, Switzerland 52%, Sweden 39%, Taiwan 32%, and Hong Kong 30%. http://en.wikipedia.org/wiki/Government_debt Plus, with the world's largest and most diverse economy, America has more wiggle room if the economy turns south.
This may indicate that US government debt is a better value than European debt. In fact, I would say that US and Canadian 10 year interest rates fall to half what they are now before I would call them at parity with the other countries on this list. So, I'm advocating increasing the proportion of your portfolio that is in US government bonds.
Disclosure: I am long NPV.