There's a line that I hear from libertarians and far-left liberals alike quite a bit: The United States wants to make the rest of the world like us. Implied here is the assumption that the 800+ military bases across the world, our presence in Afghanistan and Iraq and our primacy in immediate conflicts from Iran to Korea is a factor of pure American assertiveness and by no means an actual need.
This ignores history greatly. As World War II burgened, the United States found itself in a position of economic uncertainty, with a military that was not the foremost in the world. President Franklin D. Roosevelt said to American mothers in 1940, "Your boys are not going to be sent into any foreign wars." Pearl Harbor and the launching into war that it brought obviously changed that. After the war, Europe and Asia were a bloody graveyard of their former societies. The economies we see today in Japan and Germany, functional yet by no means perfect, would never have been created if it had not been for the United States. Neo-isolationists and revisionists like Pat Buchanan don't get this.
After the fall of communism, the role of U.S. as a peacekeeper became even more necessary. The Europeans did nothing to stop the genocidal bloodshed happening right next to them. It took the United States to end the genocide and prevent a post-Soviet upsurge in nationalism. Bringing Milosevic and his goons to trial was not a "fool's errand." It's only a pity we didn't do so in Rwanda.
Alot of this animosity towards the U.S. military and American involvement in the world seems to have been bred by the War on Terror, the war in Iraq, and Obama's continuing engagement in Afghanistan. I personally share the reservations in Iraq. When I see Iran behaving more brashly, I can't help but think of an Iranian nationalist who was at one of my classes in California. He proclaimed during class once, "I love George W. Bush! He took care of Saddam Hussein for us!" In the book The Strong Horse: Power, Politics and the Clash of Arab Civilizations, Lee Smith essentially argues that 9/11 brought America into the internal warfare of the Middle East. That's something that should make any American uneasy.
With Ron Paul and his son Rand now gaining more and more influence in the Republican Party, it's worth seeing what direction the United States will go in. Confidence in the ability to prevail in Afghanistan is slumping, and the world appears to be moving towards a status quo in which it could possibly afford to have a non-interventionist United States. China is expanding its reach in Africa, and our Canadian neighbors to the north are being found engaging our Latin American neighbors to the south. President Luís Inácio Lula da Silva appears deadset on pushing his country towards regional superpower status, engaging not only the Iranians but also in the Israelis in an effort to create another Middle East power broker in the Western hemisphere.
A world where Brazil, Canada, and/or China, among others, are filling in for the United States could be workable, even if it would mean a much less predictable outcome. These countries vary in their structure, and none are fundamental about democracy and free trade in the way that the United States is, but all are engaged enough in the world to see it in their own interest to keep that world from cratering.
Whether it's Obama or a Paulite at the helm, the image of the United States taking the helm in emerging global conflicts looks more and more like something from the past.