A variety of factors motivated soldiers in WWI, and these varied from army to army, and from front to front. We could start at the most basic level, John Keegan's so-called "trinity" of coercion, reward and intoxication. The penalty for cowardice or desertion was at most death in the case of the British army, but less than 10 percent of death sentences were ever carried out. Then there was reward, both the positive feelings of victory and "sticking it out" with one's mates (the Primary Group), and of reward for valour and bravery. Then, at the most basic level, rum rations (German and British armies), wine rations (French and Italian Armies) and vodka (Russian Army) helped soldiers to master or at least dull their fear in battle.

However, there were also more substantial reasons to fight on. The greatest problem with the emphasis on the "primary group," espoused in movies as the "fight for the man in front of you/beside you," or the "band of brothers," is that units in modern wars suffered heavy casualties, and the nature of the battlefield demanded dispersion. This was identified by Ardant du Picq, SLA Marshall and in more recent years by Omer Bartov among others. The French Army Mutinies, as well as examinations of small units in the Vietnam War, clearly demonstrate as well that Primary Group is loyal unto itself, and it's goal to survive will often be opposed to military goals. Therefor, loyalty to the battalion and regiment/brigade, as well as the division and corps (esprit de corps) was important, and can be seen in organizations like the British Regiment, the French and German divisions and corps (esp. from similar regions), as well as more distinct forces like the Australian and Canadian Corps, the New Zealand Division and French Colonial Corps, and the Russian Guards units.

National defense and war aims, as well as ideologies often stemming from ill-defined 'Ideas of 1914' played an important role here, in giving meaning to the struggles of soldiers and a framework to understand the war. Vejas Liulevicius has studied German soldiers in Eastern Europe, and found that the idea of a struggle against 'Slavic Despotism,' and even of a 'Draw to the East' did hold sway among some soldiers and officers. Russian mail censors, and soldiers diaries, also indicate a fervent loyalty to Tsardom was important for many soldiers especially from peasant backgrounds. This had ramifications for 1917, when the Tsar was forced to abdicate. British soldiers to, were exposed to a fair amount of writing and propaganda about war aims, and as Catriona Pennell has indicated in her work A Kingdom United, fear of German invasion was a strong motivator for soldiers in 1914.