World War 3
It seems that as nations grow, they periodically have monumental slug fests amongst themselves which we call World Wars. I think that as we progress forward, and resources become more scarce, we will inevitably run into a third global conflict.
First off, certain events within the last decade have pointed to this end. In 2001 the United States and its allies began to expand it's military power through out the Middle East. In 2008 Russia flexed its military muscle by invading South Ossetia, a Provence of Georgia, and nation in the resource essential Caucuses. Also, within the last several years Russia has demonstrated its technological abilities by shutting down the Internet of several surrounding countries. In 2007 China shot down one of its own satellites showing its capacity for space warfare and potentially destroying the satellites of other countries in the time of war.
Secondly, it seems that an arms race has continued to develop far past the Cold War. The U.S. as a matter of principle has continued to develop military technologies to dominate in a full out war. One of these is the USAF's F-22 Raptor which is argued to be the most lethal Air Superiority Fighter in history. As for China, last year when the Chairman of the Joint chiefs of staff visited, the Chinese Air Force unveiled its new Stealth Fighter which could be a stiff competitor for the Raptor. Also the Russian Air Force unveiled its own Stealth Fighter in 2010 with similar capabilities to its Chinese and American counterparts. Besides fighter jets all three countries have been investing in other technologies like new Submarines, new Aircraft Carriers, and new Tactical Weapons systems like Nukes, Fuel Air Bombs, and Intercontinental Ballistic Missiles.
Thirdly, as countries become more developed, they will begin to consume more non-renewable resources like fossil fuels. As these become scarce it is likely that current Super Powers and Rising Super powers like the US, the EU, Russia, China, and India will begin struggling for control of these resources for their own devices. As this happens tensions will rise, and eventually war could unravel.
So, maybe not now, or maybe not in the next 20 years, but sooner or later, a colossal struggle between nations will start once more and unprecedented destruction will occur. For better or for worse, the world would be re-shaped in a radical manner and life as we know it would change. Or maybe we'll be hit by a meteor or Jesus will return for the rapture and none of this will matter.