Imagine the Republican hatepreacher becomes President, will that bring world closer to wider conflict?
Some of the resistance movements will say: look, there is crusade against Islam. Trump doesnt deny it.
Why would this cause WW3?
You could make an argument that it might increase jihadi terrorism, but the actions of the previous 2 Presidents has also done this so no change there.
For the sake of discussion, even if it seriously damaged relations with all Muslim countries (which is unlikely as it would go against many of their self interests) this is highly unlikely to cause WW3 as they are all pretty weak militarily and couldn't do anything anyway, other than support terrorism. Lots of Muslim countries hate each other anyway so they are unlikely to have any unified policy, and even if they did join together what are they going to do?
WW3 would require hostilities between 2 major powers, probably Russia or China and America. Relations with these countries might well be
better under Trump as he might well replace the current ideologues driving the antagonistic US policy towards these countries.
Electing Trump might well make many people around the world view America (even) more negatively, but it arguably reduces the chance of WW3 when compared to a Clinton presidency.