Japanese Prime Minister Naoto Kan bows after giving a speech at the Democratic Party of Japan lawmakers' meeting in Tokyo Friday, Aug. 26, 2011. Kan announced he was resigning after almost 15 months in office. (Koji Sasahara/AP)

Japanese Prime Minister Naoto Kan announced his resignation Friday, ending a 15-month tenure defined by crisis and opening the door for this country’s seventh leader since 2006.

Kan’s decision to step down, the fulfillment of a pledge he made in early June, marked the inevitable endpoint for a leader who had failed to galvanize a stricken nation. His departure further extends Japan’s search for a prime minister capable of tackling, rather than getting tackled by, its many fundamental problems.

Kan’s successor, to be determined in a ruling party election Monday, will inherit both Japan’s slow-burning economic woes and the urgent reconstruction challenges brought on by the March 11 earthquake, tsunami and nuclear power plant disaster.

In the aftermath of Japan’s greatest crisis since World War II, critics accused Kan of inability to lead a coherent government response. But even with the unpopular Kan out of the way, Japan still has a divided parliament, a shrinking population, a soaring debt, a strong yen and potential energy shortages that could force corporations overseas.

It also has no clear-cut successor to lead it.

After the Democratic Party of Japan selects its new president Monday, the winner will become prime minister. Japanese media spent much of this week describing former foreign minister Seiji Maehara as the front-runner.

But the equation shifted Friday, when party power broker Ichiro Ozawa threw his support behind Trade Minister Banri Kaieda, whose ministry is responsible for the promotion of nuclear power. Although Ozawa has been suspended by the DPJ over his alleged role in a fundraising scandal, he still controls a faction in parliament.

Kan said Friday that, given the “severe circumstances,” he felt he had done his best. “Now I would like to see you choose someone respectable as the new prime minister,” Kan said.

Since the departure of the popular Junichiro Koizumi in 2006, Japan has had five prime ministers, Kan included. Only Kan lasted longer than a year.

He took over in June 2010, replacing the unpopular Yukio Hatoyama. But Kan himself squandered popularity within weeks, facing criticism for his flip-flopping over a possible consumption tax increase.

At the time of the 9.0-magnitude earthquake in March, Kan was days away from stepping down. But the disaster, and the short-lived political cooperation that ensued, gave him a second chance.

Post-disaster, the former activist emerged as a sharp critic of Japan’s powerful nuclear industry, which has long enjoyed a cozy relationship with the government agency designed to regulate it.

Kan told the nation in July that he favored a nuclear phase-out — meaning Japan should eventually shut down all of its 54 reactors. But even with a majority of the country backing such a policy, Kan was unable to translate that support into political popularity.

Fellow lawmakers blasted him for speaking his mind without consulting others. And in the meantime, the government struggled to convey understandable and timely information about the unfolding nuclear crisis.

In a televised address Friday, Kan expressed hope that Japan could realize a future in which it is less reliant on nuclear energy.