Kagan argues that the world is not divided by religion or race as Samuel Huntingdon's 'clash of civilizations' theory suggests and the modern trouble with Islam/West seems to vindicate. Rather he argues the real division in modern geopolitics is between democracies and autocracies, with places like the USA, Europe and Japan on one side, and countries like China, Russia and Iran on the other. As he explicitly states in the book, "But in today's world, a nation's form of government, not its `civilization' or its geographic location, maybe the best predictor of its geopolitical alignment". For example, China and Japan may have a shared Asian culture, but one is a democracy and the other is an autocracy, therefore, Japan will have more in common with another democracy, even if it is not culturally similar, that it will with China.
He argues that the autocracies are dangerous, not just because of their oppressive internal policies, but because they typically are experiencing rapid economic growth. This allows them to fund a more powerful and threatening military with which to threaten democracies: Russia's booming oil wealth has seen it pick fights with the EU and send nuclear bombers on training runs on Western cities, and China makes increasingly murderous demands on Taiwain. Also their economic success in the absence of democracy could lead other countries to emulate their autocratic rule as a means of imitating their success, and there are the beginnings of this in places like Venezuela.
Kagan acknowledges that one autocracy can have friction with another autocracy: for example, Russia and China may distrust each other over their mutual ambitions in Siberia. He also acknowledges that democracies can have friction with each other: for example, the bitter exchanges between the US and France on the eve of the Iraq war. However, Kagan's key point is that when push comes to shove, a democracy will always side with a democracy in conflict with an autocracy, and an autocracy will always side with an autocracy in a conflict with a democracy.
Perhaps most controversially, Kagan accuse the UN of sheltering autocracies under the guise of sovereignty. Also, China and Russia are permanent Security Council members with the veto, and thus can protect other client autocracies like Sudan and Turkmenistan from UN action. To solve this, Kagan advocates setting up a "League of Democracies", where democratic countries can co-ordinate policies for dealing with autocracies that compliment the UN, but which in fact will probably be an alternative to it. He claims the autocracies have already set up a "League of Autocracies" under the guise of the Shanghai Cooperation Organisation, which in his eyes is nothing more a Warsaw Pact for the 21st century which needs to be countered.
The book is not without weaknesses. Firstly, Kagan's plan for a League of Democracies is unconvincing on two levels. Firstly, it is hard to see how such a structure could be set up without it being seen as an alternative to the UN rather than a compliment. Secondly, democratic countries often have rivalries and friction with each other, for example France and America have a mutual hostility, and bitter memories of their clashes before the Iraq war. Kagan seems to dismiss these as trivial rivalries, but it is hard to see how such clashes would be avoided within his League of Democracies. Kagan's dismissive claim that democracies will overcome these due to greater fears of the autocracies are, in my view, unconvincing.
All in all, the book is an interesting overview of a reality that undoubtedly puzzles some political thinkers, and is well worth a read.