A world war? I don't think that Syria or Iran can strike and attack Europe or America. It is not a world war because it is a war between countries from all over the world. It is a world war because the war happens everywhere in the world, which is not gonna happen.
If america attacks syria, Russia will attack america because that attack would be Illegal, if america is going to do shit on its own while the other countries must follow the world law than they will surely attack america and back syria. all of the american allies. if america even has allies anymore will back america while all of russia's allies will back russia, maybe china will back russia or the other. North Korea will surely get involved and take this chance to attack south korea, Japan will try to back south korea because they both hate the north koreans and chinese. and the arab countries will wipe israel off the map. and the Israelis being the sociopaths zionist they are will likely launch the samson option.