Old-ish (and not necessarily politically correct) literature often asserted the relevance of national traits in armies, even in individual soldiers.
A typical description for a British soldier would be 'stubborn in the defence', or an Italian as 'brave, but doomed due to poor material'. Outstanding are the rich depictions of the Russians, who impressed German WW2 officers a lot. Their published stereotype was 'close to nature, and thus good at camouflage', 'able to withstand great hardships and make do with primitive means' and similar. Every positive mention of Russian soldier traits sounds to me like a description of their superiority, not like an attempt to save their face (as with Italians and Romanians, who seem to have been defended by German WW2 officers against critics).*
The actual accuracy of such stereotypes is by now only of interest for historians, since no doubt the societies, upbringing and cultures changed a lot.
Yet the concept of national traits may to some degree be true, and thus of interest today and in the future. Yet, how to learn about such traits short of waging war?
One approach could be to look at simulated warfare, and since hardly anyone has a close-up vantage point over actual military exercises (not the least because there are very few large-scale outdoor exercises nowadays) we might look at the next-best simulation: Computer multiplayer games. These bring together players from different countries and by the very large quantity of players and matches there ought to be fine statistical relevance for this demographic. Many so-called "Russian" gamers are often Ukrainians or other people (even Greeks, since "Russians" are usually identified by chatting in Cyrillic), though.
I'm focusing on Russians here because they are of particular interest to a defence-interested citizen in a NATO and EU country. I've looked this up and the stereotypical Russian player seems to differ from game to game.
In some games, Russians appear to have the reputation of being incapable of teamplay, in others the opposite. It appears that the language barrier is the actual determinant here: All-"Russian" teams appear to have teamplay, whereas "Russians" in a mixed language "team" are reputedly incapable of teamplay. It should be noted that teamplay doesn't require a player to communicate in game chat; he could adapt his actions to what the majority does - and seemingly they don't.
The observation becomes particularly difficult and anecdotes may be misleading because players aren't equal. The game developers know that about 5% of the players can wipe the floor with the other 95% any time in a 1-on-1 contact. There can thus be some very impressive players of nationality "A", while the vast majority may appear to be useless. The experience with players from country "A" depends thus on whether you have a systemic bias in your contacts. Top players teaming up with other top players will meet a disproportionate share of very effective players from "A".
A few quick observations and internet text searches are no proper way to research the topic, and nobody should build his own prejudices about a nationality based on such a superficial research. My point here is that people who actually get paid to do research might gain some useful, statistically relevant insights by observing different nationalities in MMOGs and MOGs. They might be able to define a set of psychological archetypes (or adopt such from less specific psychology theory) and observe players from different nations to determine the different shares of these archetypes in different nations. This might actually be of use for military theory, specifically doctrine development and red teaming/OPFOR. We sure should not rely on generations-old stereotypes or Cold War prejudices.
*: It's the negative attributed traits more than the positive ones that make the written stereotypes look racist and politically incorrect in the post-Cold War world. Many if not all stereotypes have at least a small core of truth, though..