[Symmetry]

Actually people tend to really overestimate how important trenches were to the stalemate. Sure, it took a lot of effort to break through a trench line but both sides were perfectly capable of doing it when they could devote enough resources. The problem was that railroads meant that the mobility of the defenders was always much greater than the mobility of the attackers and telegraphs meant that the abilty of the defenders to coordinate was much greater than the ability of the attackers to coordinate. The internal combustion engine and radio changed this when WWII rolled around.

There were also very many places where things could have turned out differently. For instance, if the Germans had stuck to the original Schlieffen plan and managed to outflank the allies they might very well have captured Paris right at the start.