The situation now is starting to look more and more like that on the eve of World War I. It is often thought that the rise of Germany was the main cause but I think the general climate in that period was more important. Geopolitical changes like the rise of Germany are happening all the time. What differs is how people deal with them.
Before World War I there had been a long relatively peaceful period and nobody expected anything serious. People were very nonchalant about war. There were even reports of people celebrating when their country declared war and the general expectations were that within a few weeks "our" troops would be home celebrating victory.
We see now increasingly the same thing happen. The speed within which the US undertakes new wars keeps increasing while its respect for international treaties and organs keeps diminishing. And the recent enthusiasm in Europe about the Libya war and Germany's behavior in Kosovo show an increasing war-loving Europe too.
In 1914 it went wrong when the adversary proved too strong and the diplomats were incapable of finding more peaceful solutions. Now the West may one day find itself facing China or Russia and have the choice between real war and compromise. It might well end up with real war.