Communists want America, and have been corrupting America, they will likely eventually try to forcibly take us, but they may not have to. China may decide they want us to pay our debt and fight us over it. America is the central non-socialist/communist country, and is going to get in the middle of a war unless that changes (which it is, somewhat).
US invades Iran for their oil and attempts to Change the Petrodollar, China and Russia have stated they would not tolerate this, causing mass scale warfare to break out, Between America,NATO, Israel VS. China, Russia, Middle eastern countries, North Korea, Some South American Countries. Drawing in almost every superpower in the world and toppling many smaller countries and causing a lot of death and damage to the world
While things may seem bad on the news all the time, in reality, I think a WW3 is not very likely. Since the rise of the UN, NATO, and other multinational alliances a war on the scale of WWII or WWI has never happened or even came close; despite the Cuban Missile Crisis which was solved before there was an armed conflict. But if there were a WW3 the United States would definitely be involved one way or another, but I do not think the U.S. would be a cause. American conflicts since the fall of the Soviet Union have been focused on counter-terrorism rather than against other countries unless they work with terrorist organizations like Iraq. Unless terrorism is a major player in WW3 I do not see the United States being largely involved in causing it.
While there are some exceptions to this rule most people in power (specifically dictators, but really any government), don't want everyone to die (no one to rule over). Because of this there is a very strong incentive not to fight on a global scale like that of WW1 or WW2. This, coupled with nuclear weapons that can hit any country, and the USA with it's large (arguably too large) military and you get an environment that make world wars unlikely (but not impossible). Also, since American is a democracy, I would like to think that they would think twice before starting a war in which there can be no winners.
I think the world has learned from it's mistakes, and as stated, organizations such as the UN and NATO have been formed since then that would discourage a large-scale war. Also, with such economic interdependence, a world war is a lot less likely. To add onto that, attacking a nuclear armed power could employ MAD, resulting in a stalemate. America has no incentive for war, and it's allies would likely abandon it if started one.
The U.S. will more than likely be involved, but I don't think we will be the sole cause. It will be a conflict of interest, perhaps over religious ideals, or even greed (over oil reserves) that will cause it. I also suspect that Russia will get drawn into this conflict. The Middle East has had a lot of problems in recent years, and I think something will happen over there that starts another world war.