I can tell right from looking at it that this art has power behind it. Through moving words with interesting font to the simplistic background. Being a motivational poster to the simple mare, this screams Strength, Honer and Dignity. Though I am not for some vector styles you sure have pulled off with this pic congrats. I feel as though the tank is placed in an awkward spot in the background as though it is connected to the gun. Also seeing other pics of Equestrian War stuff I might have to doc a few points on originality. But over all this is a great pic.
The flag is awfully nondescript and its relatively bright color stands out against the otherwise stark palette of the rest of the piece. I see what the artist was going for, but a solid red flag isn't the right way to do it.
I knocked a couple stars off for originality, but it is an homage to the sort of war time effort propaganda, so that's just the nature of all such allusions.
I'll have to bean the artist on credit as well, because since the focus is on nurse Redheart, she should be the most prominent figure in the image. The ideal posture should be of her playing as the guardian of the frontline soldier, either standing high above Dash or deeply entrenched with the soldiers tending to them. Also, Dash should have a Russian firearm instead of an M-1 Carbine, as it was a distinctly American gun, and easily recognized by even amateur war buffs. Finally, wartime propaganda depicting battle would usually have them facing left, or West, as the Russians were defending themselves from the German invasion which was coming from the West, which became a considerable symbol in Soviet society after the war, despite the fact that America was actually closer from the east than west. This last point I didn't really knock a star off because it is ponies.
Finally for impact, it would be better received if the technique were improved, but I can't see any way to give it 5 stars because personally I don't condone the idea of war and ponies being combined, even in fanmade hypothetical situations.