By 1900, European armies had transitioned to vast armies of trained regulars and conscripts. Despite his status as a entertainer rather then a historian, Dan Carlin expressed First World War European armies (continental armies that is for Britain's army was distinct in that it had a regular standing army at the outbreak) as heavy weight boxers. They could take a punch, rally and come back to the fight, they didn't suffer a single knockout hit and that was it. The French, the Russian, the Austro-Hungarian and particularly the German armies all suffered horrific blows during the course of the war that would have seen any army prior to 1900 (except maybe Napoleon's) unable to continue fighting. This was made possible by the largest utilisation of conscription up until that time that allowed armies to replenish their losses for a time (eventually all sides would feel the impact of dwindling manpower resources).

Additionally, the lack of manoeuvring room for armies on the Western Front due to the nature of modern warfare meant that neither side was able to achieve the knockout blow required to force the other to submit or withdraw. Both sides tried it, the Germans against the French at Verdun in 1916 and the British against the Germans at Ypres in 1917. Neither managed to achieve the attritional victory they desired and both did exceptional damage to their own armies trying it.

The German army was also extremely adept at fighting a defensive war. They made effective use of whatever high ground was available even withdrawing to high ground if it meant they would have been in a better tactical position. After The Somme Offensive in 1916, the Germans also adopted a defence in depth. This means that instead of placing all their manpower in the front line trenches to resist an Entente attack, they would lightly hold the front trench and maybe the successive trenches while most of their forces would be held back in reserve trenches. The Entente attackers could take the front trench and continue their advance into the German lines whilst taking casualties from artillery and machine guns until they were worn down and had outrun their own artillery support. The Germans would then launch their own counter attacks, pushing back the depleted attackers and retaking the ground. This is a very simplistic explanation of defence in depth and doesn't do justice to the monstrous complexity the Germans applied to their defences which were sometime kilometres deep. The most famous example of German defence in depth was the Siegfried Line, known to the Entente as the Hindenburg Line. This line of fortifications served as the principal German defensive line from the start of 1917 to the lines breaking in late 1918. It was an immense undertaking and was resistant to all attacks launched against it until sophisticated cooperation between artillery, tanks, infantry and aircraft was developed in mid 1918. By that time as well, German manpower shortages was becoming an issue, as was morale and the poor supply situation in Germany due to shortages provoked by the British naval blockade. Unrest in Germany did just as much to bring Germany to the Armistice table then the Allied advance in the latter half of 1918 did.