Why no trench war?

Why didn't world war 2 end up in a trench war? Was it the use of new tactics, weapons or technology?
 
Mobility, communications, firepower, tactics.

in WW1 MGs improved defensive whileoffensive lagged behin until massive use of tanks. Arty didn't work, neither did gas. In WW2 offensive had the edge with armor and combined arms. communication allowed attackers to keep up the momentum as advancing units could inform HQ where they were, how to shift fire, what to reinforce.
 

Dialga

Banned
I'd have to say it was mainly due to the large-scale use of tanks, bombers, and (to some extent) aircraft carriers.

Men in trenches would be sitting ducks to a bomber.
 
First of all, only the western front was locked in trenches in ww1, and to some extent the Italian front. The eastern front, the serbian front, the Palestinian front, the Kut front etc all moved quite a bit back and forth.

Secondly, the reason the front stagnated between autumn 1914 and spring 1918 was mainly due to the concentration of artillery - no where else, before or after, have such an concentration of artillery per km of frontline been achieved over a large front. Another reason was the advantage of mobility of the defender - artillery had a limited reach. As soon as the forces breaching the frontline reached the position beyond their own artillery's reach, the encountered a new line covered by enemy artillery. It was quick to move reserves by rail to a threatened front, while reinforcements for the advancing party had to move over the devastated no-mans-land. Especially artillery and its supplies was hard to move this way.
 
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