Don't completely discount the idea of "glory in battle". In the U.S. especially, look at, for example, the U.S. Marines- "the few, the proud", "looking for a few good men" "first to fight", etc.

It really depends on the specific military involved, but in a far looser sense, much of that emphasis on glory in battle and an honorable death is a product of the rise of the middle class and jingoistic nationalism, basically from 1850's ish to the end of WW1, for the Allies and WW2 for the countries that made up the Axis powers.

Previously, in most countries military service in the standing army (not in cases of being drafted) was primarily an experience for either the wealthy, who could afford to buy or have connections to get a nice officer rank, or the very poor who turned to the army life out of desperation. The idea of serving your country by joining the army is mostly one that develops first in France during the desperate periods of the early Republic and then spreads throughout the continent thanks to the rise of nationalism.

It is then that this idea starts to really spread into the lower middle classes, which is where the concept of glory in battle and honorable death takes its strongest hold. The poor can be enticed into service thanks to monetary factors and the need for work, the very wealthy can be brought in because they are assured of at least a nice head start on a career. The lower middle classes have neither of these two needs, and as such they need to be brought in with ideas of glory, self actualization and other forms of emotional ties. George Orwell addresses this in his essay on Rudyard Kipling, as well as several others where he talks about the "blimps", lower middle class military families.

To bring it all back, WW1 is really the death of this idea, as in many ways it was the death of French and British jingoism. It wasn't so much the intense death and destruction of the fighting so much as the fact that France and Britain were so spent and were no longer in a place to expand. Jingoism is an idea that is fueled by the possibility for expansion, usually in the form of large amounts of land ripe for the taking. However, the post WW1 world was much more solidified, with increasingly large amounts of the world either under control of stable forms of government or part of a colonial state. This means that there was no longer a wild frontier to explore and ideas to push forward. Plus, the myth of French and British strength had been broken by the fact that Germany had taken on France, Britain and Russia (doing the lion's share of the work) and had nearly won. Whereas before you could speak about the glory and strength of France's soldiers, the fact that the Germans had nearly broken into Paris caused a severe shock to French self confidence.

In short, while people tried to keep the ideas alive into the second world war and beyond, most notably Winston Churchill, the lower middle class ideas of glory and honor in battle died alongside French and British jingoism and that's what caused the transition in emphasis in recruitment. Now we've returned to the far older model of promising a career and economic stability to soldiers in return for national service. In essence, we've expanded the recruitment model for the poor to the rest of society.

I think WWI for European powers was the big killer: Decimating an entire generation of young men. For America, coming late to both WWI and WWII when they were the defining factor, I would say the Vietnamese war was the real turning point for public opinion on such matters of "honour and glory"