At one time fighting in a war usually came with a lot of honor, possibly some money if you managed to take some of the rich dudes prisoner (the ones with house banners and horses tend to be these guys), and fighting in battles was a sure way to at least push back approaching armies and protecting your homes.

In the present people don't carry house banners, just country flags. Prisoners of war don't tend to net any money for the soldiers who capture them since handing out medals is cheaper and doesn't run the risk of a soldier selling a real villain back to their country. While soldiers fight ground battles still, most notable military attacks involve missiles and bombs, two things that ground troops have no hope of preventing from reaching their families.

Making better weapons will have the effect of making older weapons obsolete unless they change fast enough. Humans in war are a kind of weapon, since more of them can change the course of battle. Therefore, humans cannot participate in war and remain a powerful weapon forever. We have already passed that point, with certain weapons being "unusable" in war simply because they are made specifically to kill people as fast as possible, like certain chemical weapons or the use of nukes. The first country to aim for defensive rather than offensive technology will be the one to take over the world, because powerful weapons are unusable.