> If talking Germany the basic example is changing from a very militaristic society (far before the Nazis) to a rather pacifist society.

I seem to recall that this was not the result of Germans staying put and changing things for the better, but rather due to external forces reducing the majority of their country to rumble and and spending 2 decades reeducating them.

Not sure what "your country" is, but here in Germany that's the general consensus of Germany's progression to a "rather" pacifist society. You might want to take pacifist with a grain of salt though, considering how excited many Germans were about being able to deploy the Army for non defensive reasons in the Balkans, Afghanistan, etc. and how giddy everyone was that we were once again allowed to export arms to Ukraine. Not to mention the current rise of far right, xenophobic parties.

Fighting corruption is very difficult. A good way to go about it is to sent some of your young people to countries that don't have massive problems in order come back home viscerally convinced it's not a necessary evil you need to put up with.

> considering how excited many Germans were about being able to deploy the Army for non defensive reasons in the Balkans, Afghanistan, etc.

Having lived at that time in Germany, I can tell you how excited many Germans rather were to openly name the responsible politicians "war criminals" (and would have been insanely happy if these politicians were brought before a war crimes tribunal) and the compatriot soldiers to participated in this campaign "murderers". I know this very well because I was among these people.

Even on the schoolyard there was a deep divide between the boys who were not completely rejecting the idea to do their (at that time near-compulsory) military service instead of considering at most doing alternative service as the only acceptable alternative, and those who did alternative service did then use every available opportunity to spread their opinion about wars and the military (they often had to work their alternative service in some welfare facility or retirement homes - places where you meet lots of people to whom you could tell your "soldiers are murderers" opinions).

The way I see it is the cultural change happened after the Prussian elites lost power and the general German public understood their recent history as far from the eternal victory they were promised. That's a major cultural change however you want to spin it, and there are enough examples in history where countries haven't gone through the same changes in similar situations (Weimar Republic also comes to mind)

Regarding the current day pacifist state of Germany, in my mind it is still very drastic anti-militaristic compared to the vast majority of the world.

Regarding corruption, countries changed drastically during the 20th century due to ideologies and individual action, sometimes resulting in disaster but also often not. Trying to say nothing can change is a defeatist deterministic attitude that has no anchor in recent history.

Presuming we are talking about migration, most of these source countries were able to fight and win European colonization in the past, why do you think that's easier than fighting corruption?