I hear a lot about the trenches and No Man's Land of WWI, but never anything about why it was such a common tactic. Had other armies used it in the past?
I'm sorry for my writing being so choppy / bad, I'm writing this extremely tired but I still want to get a general idea out there. If you need me to delineate on anything specific just ask and I just beg your preemptive pardon.
We need to clarify some concepts here first. Trenches being used a defensive fortification would be hundreds of years old by the First World War. Even as early as Medieval Warfare trenches and underground tunnels would be built for communication and to mask movement and general posturing to essentially lock down a city. Trenches were not an unknown tool by the 20th century and like I'm sure many will bring up were used in a limited fashion in the American Civil War and Franco-Prussian Wars. However, those trenches shared one major trait; they were temporary and used for the engagement at hand and then abandoned.
What makes the First World War so distinct with its trenches is the permanence of them. They would extend from the beaches of Belgium in a continuous line down to the border of Switzerland and would remain and be continuously fortified for nearly four years. Trenches would be sophisticated and their construction would be turned into an art. It's absolutely mind boggling just how extensive these trenches were. We tend to think of the Western Front as two lines just kind of staring at each other but it was more than that. It was all those lines with dozens of underground communication tunnels and supporting trenches and offensive trenches and fallback trenches and communication trenches. It wasn't just two super beefed out lines looking at each other. You can see from that sample I just posted -- these lines were deep and would sometimes extend a kilometer deep of twisting and turning with hundreds of miniature trenches.
Why it happened is a pretty easy thought exercise and overview of events. The Germans would open the war with a massive offensive that would push the French to the outskirts of Paris. The French would perform a counter offensive that would push the Germans near the border of Belgium. The Germans began to dig in so they wouldn't be pushed back further. Both sides tried to get around the flank of the other to get an edge and go back on the offensive, thus titled the "race to the sea" as both armies literally raced to the coast of Belgium to get around each other -- unsuccessfully. They would literally stop on the beaches. Not being able to get around the flank of the other and suffering massive casualties in the opening months of the war, both sides would begin to dig in.
There was no day both sides agreed to make trenches, it was a gradual transition. You know those DirectTV commercials that start out with a guys cable not working and it ending with him being body slammed by a gorilla? It's a tongue in cheek example but this really summarizes what I mean. You start out with a bunch of dirt trenches. You throw on some sand bags and machine gun placements. You're gonna be here for a while so you make a few underground tunnels and some barbed wire fields and create some latrines. Well now we're really gonna be here for a while so we might as well build even more trenches to house even more men and move around safely because of all these damn snipers and artillery shells.
With this newfound "safety" came extra time of largely sitting around. You didn't need to go out on patrols or keep moving the front or what have you -- you improved the trench. You weren't put out to attack the other trench every day, that's silly. You sat around all day trading shots with the other trench and making your side even stronger. You would begin to get worker parties who would go out at night and reinforce the barbed wire damaged by artillery the day before and lay mines. You would have men start reinforcing trenches with wooden beams, drain water, create rudimentary latrines and tunnels for safety and importantly sleep and protection from direct hits. Snipers and stray artillery shells are still an issue though so you create "vertical" trenches that go back to other "horizontal" trenches so that you can at least sort of safely move between layers of the defensive line. You also zig-zag them so that if the enemy does get a lucky direct hit the shrapnel is confined to a small section of the trench.
Well now we both have two sides with ludicrously fortified positions across an entire front staring each other down and no real way doctrine or technology or combination of the two to allow us to break through. Over time strategies will be devised, technologies introduced, and doctrines expanded upon that would allow for trenches to not only be tackled but rolled over like warm butter. However until then the two sides had no option but continue fortifying and performing costly campaigns to just get a little better positioning that would allow your side to wear down the enemy faster and make them give up or be too weak to defend.
Notes:
Doughty, Robert A., Pyrrhic Victory: French Strategy and Operations in the Great War
Simpson, Andy, Hot Blood and Cold Steel: Life and Death in the Trenches of the First World War
