Everything in our modern society is based off of oil, which is why everyone feels the crunch when oil prices rise. Shipping, and therefore the prices of every good you buy in a store, is affected by fuel costs. The list goes on, but Klare is a much better linguist and scholar than I, and explains oil's importance in the introduction to this book.
Because of its importance, which is really the main point of the book, is that oil is the one resource that has been deemed a matter of national security. Due to this, the government can use oil as a reason to use the military wherever it sees fit. Putting aside the obvious relation to the Iraq War (which is not the focus of this book, which I liked), the United States supports many countries, namely Saudi Arabia, due to oil. But I will not go into a summary of this book, which you could probably find on sparknotes. All I would like to say is that this book has a great balance between history and current events to be both nonpartisan and interesting.
To give my own opinion, this book is a must-read. Before I read it, I never understoof why people always claimed that the Iraq War was started over oil. But now I now understand the argument, and whether or not you agree with it, this book will show you the reasoning for it. But I think that it was quite nonpartisan, criticizing FDR just as much as George W. Bush. And most importantly, Klare does not merely say that the current situation is bad, but he actually produces some ways to fix it. Klare explains his points well, with intelligence and articulation. The bibliography is huge, and it contains a nifty index. I'm definitely going to read some more stuff by Klare, or on the subject.
Here's where you can buy the book (I bought it at Barnes & Noble for $16):