Last month, the credit rating agency Standard & Poor’s lowered its outlook on U.S. debt to “negative,” suggesting that the United States’ top-flight “AAA” credit rating is vulnerable to a downgrade, which could send interest rates up, make it hard for businesses to get capital, and put the brakes on economic recovery. But the U.S. isn’t alone; here’s a look at where other major world economies rank on the credit rating spectrum, plus an sampling of smaller countries whose shaky ratings put them in the category of “speculative” investments.