Reports of atrocities and the invasion of Belgium don't really imply nationalism, or love of king and country to me. If anything, they imply the opposite; love and support of another country.
I'm trying to put myself in the shoes of those who enlisted, and ask; what would my motivations be?
Empathy and compassion for the victims of the escalating war, stopping an 'evil' force before it gets too close to home, maybe just a vague sense of morality- sticking up for an underdog.
For me personally, it wouldn't be a love of a state or it's monarchy.
I'm assuming from our exchange that your a patriotic person - where does that come from? Do you love the queen, the flag, are you proud of England's "accomplishments"?
I'm not being glib or argumentative by the way, i just genuinely don't understand why someone would love a nation.