WASHINGTON—The recent extradition of former Peruvian President Alberto Fujimori to face charges of human rights violations and corruption is a welcome development. It is also a monumental challenge to the institutions of a country that has not been able to establish the rule of law as successfully as it has been able to generate economic growth in recent years.

Among other charges, Fujimori, who was extradited to Lima by Chilean authorities, will be tried in relation to two civilian massacres at the hands of a military death squad active during his regime. His political organization—mostly a collection of relatives and cronies—is using its 13 members of Congress to pressure the government and the magistrates to set him free.

Some Peruvians rationalize the human rights violations and the corruption of the Fujimori years with the argument that the country was at war with the Maoist terrorist organization known as Shining Path and that his government spurred the economic recovery of the last decade.

The greatest challenge in the upcoming trials will not be political pressure on judges or the publicity of a highly charged case at a time when global financial institutions are on the verge of granting Peru an investment grade, the highest economic rating. The greatest challenge will be testing the Peruvian people’s capacity to decouple in their minds their personal views of Fujimori’s government from the moral and legal implications of the crimes for which he will be tried.

The capacity or incapacity to make that distinction will tell us whether Peru has gone from being a society that puts institutions and moral principles at the mercy of political necessity—the mark of underdevelopment—to a society that embraces the principle that the law is an impersonal set of rules over and above personal preference, political convenience or sheer passion.

Because many Peruvians were not ready to make that distinction in the 1990s, Fujimori’s government was able to concentrate colossal amounts of power with popular support—hence the crimes and the corruption for which dozens of his former collaborators have gone to jail. There was a time, shortly after Fujimori fled to Japan and resigned his post by fax in 2000, when many Peruvians, shocked by spectacular revelations of high-level corruption, seemed ready to understand that accountability, limits on government, and the separation of powers are extremely important. However, with the passing of time a substantial number of people have started to forget the tragic events of the recent past. Even if they distance themselves from Fujimori personally, they seem to advocate, for instance with regard to law and order issues or the uncomfortable presence of NGO activists in parts of the country, some of the dictatorial tactics that made human rights violations and corruption systematic in the 1990s.

The mental transition from the idea that strongmen are the solution to a nation’s problems to the idea that impersonal institutions should be more powerful than those who rule is crucial. Much of the progress that has taken place in the world in recent centuries stems precisely from that transition. The countries that have not shaken off the tradition of strongman rule need to learn not to subject basic human rights to the whims of politicians acting on a wave of popular fear.

Peru is undergoing Asian-style growth rates and its entrepreneurial class is rapidly adopting new technologies and becoming competitive. But the other part of the development equation—decoupling the institutions from the political process in order to protect individual rights permanently—is not yet fully in place. That is an age-old cultural trait that will need to be overcome through leadership and reform.

One way to start is to show the population that Fujimori’s trials are not part of any political revenge and that he will be treated more fairly than he treated his enemies. But Peru’s still precarious judiciary will also need to show that it is ready to do its job impartially, no matter how much political pressure Fujimori’s supporters bring to bear.