In the last century, there were 3 european nations that had major changes in their political climate. There were more, but i'm focusing on these 3 for the lessons we can learn.
All of these were coming out of a monarchy system of govt. The people were tired of the corruption, the injustice, & the inequality that this system had perpetuated for generations. During the turmoil & upheaval of change, there were many voices clamoring for power. Anarchists were active, blowing up govt buildings, battling with police, & creating mayhem. There were socialists/communists in all of them, actively working to consolidate their power & build their view of the ideal human govt. Fascists were also competing for their slice of power. They were the ones rallying the people behind nationalism & racial superiority of their people. And there were also the monarchists.. those who supported the old system & wanted to return to the old ways.
These were significant world powers. Spain had ruled the world in the not too distant past. A major world war had been fought in the previous generation with Germany being the aggressor. And Russia had been simmering in political upheaval for years. But the main point is the result of the upheaval in all of these examples.
Russia turned to collectivism. The communists were able to consolidate their power, & gained control.
Germany went fascist. Hitler's nazis gained control, & ousted the commies & the old guard.
Spain's Franco used military dictatorship to squash the communist & anarchist uprisings, & kept many of the old ways, supporting the monarchy & the ties to the church. Spain had the most involvement from outside, with many internationals fighting for communism, but germany & italy helping franco.
We tend to focus on hitler's success, since it affected the rest of the world so intensely, but all are interesting examples. Russia had nearly a century of communism, but it eventually collapsed & broke into smaller states. Franco ruled spain until the 70's, when he died, and he tried to set up the old monarchy again. But it went through a democratic process, with plenty of competing voices clamoring for power. It is still pretty much in transition.. the economy is in shambles, & there is no political identity that has a consensus. Anarchists have a large constituency there, as well as the collectivists, & the traditionalists. Germany had a very interesting transition, from a dominating world military, to defeat, to rebuilding, to currently, the most successful economy in the world. They have stayed with the democratic process, which was based in part on the success of the usa & their constitution. But it was the german people & their industriousness that lifted them from the rubble of war.
The lesson i glean from these historical examples is the continued success of a democratic republic. Collectivism, fascism, anarchy, & reactionary moves do not provide the prosperity or the freedom for the people, like is found in a democratic republic. When the people are allowed to work & keep as much as their labor as possible, the nation flourishes. But when the people are taxed oppressively, or forced to labor for the state, they languish. All nations are always in transition, & nothing stays static. But people who do not learn from history, are doomed to repeat it.