During WW1 and WW2, the battle was between opposing forces that were near equal in power (depending on who vs who). For instance, Germany was going against multiple nations that had to join up to even rival Germany's power. In my opinion, a World War that we would even care about or classify as a "World War" are between the worlds most powerful countries that can cause untold effects to countries and landscape around them.
These middle east countries are small, their military power is weak, their people are scared and cannot be relied upon, etc. It might be a massive war but I won't call it World War 3. Now, if it were China vs USA, that's a completely different story. Those 2 countries going toe-to-toe would cause more deaths, more destruction, more everything than every middle east country combined.
Furthermore, if America were to fight alongside Israel in a full on war, the opposing forces might as well say their prayers. I'm not hyping up America, but to fight one of the top 3 most powerful nations on the planet is suicide.
