[cnelsenmilt]

What measure are you using for "largest"? The US is 3rd in the world by population and 1st by GDP, so in absolute terms it's to be expected that they would be "large" in many categories, simply by having more people and money. (And then there's geographical extent.) The relative (per capita, perhaps) measure is more salient.

[yucky]

Based on books in circulation (overall and per capita). Also for anybody who isn't familiar with interlibrary loans, check it out. In the US you can get access to almost any book around the country sent to your local library. The system is amazing.