It's true on the relationship between states while social effects linger for much longer. For example: there's still plenty of animosity from Polish people towards Germans, not in a violent way but more as a priori background distrust of German actions, any perceived transgression has a much bigger backlash than towards other nations due to history passed down by generations of people telling each other about the horrors their ancestors suffered.
It's the kind of thing that takes centuries to fizzle out, like between Denmark and Sweden, after 200-300 years the wars waged before that are mere historical artefacts used for jesting. If Denmark had been on the Axis-side willingly and tried to invade Sweden in the 1940s this would be a completely different relationship.
So yes, people will overcome historical grievances but it might take many generations, for us living right now it might not ever happen before we are dead.