If the United States has the largest economy in the world and Japan's is second, it is very much worth Americans' taking a close look at what just happened in Japan's elections. If that is too abstract to focus on, then let's try the fact that Japan holds at any given time more than $700 billion in U.S. treasury securities, close after only China in that regard. In other words, Japan's health is America's health.

What the Japanese electorate did in Sunday's elections was to turn out of office the Liberal Democratic Party, the party that has led Japan almost without respite since 1955. (The LDP's hold on office in Japan is comparable to the Democratic Party's in Pittsburgh.) The turnout was gauged at 69 percent. It was a landslide -- or, in Japanese terms, an earthquake. The LDP party leader, Prime Minister Taro Aso, resigned, taking the hit for his party's crushing loss.

The winning party, the Democratic Party of Japan, took 308 of 480 seats, giving it a clear majority in the lower house of parliament. Its leader, Yukio Hatoyama, 62, studied in the United States at Stanford.

The focus of the elections was the current economic recession, which has hit Japan hard. The longer-term context of the LDP's overwhelming defeat is the sense among Japanese, based on almost two decades of relative economic stagnancy, that their country is in decline -- in both its standard of living and in its standing in the world.

It was interesting and predictable that this led to a tidal shift at the polls. It is even more interesting that, as a people who are basically conservative in their social mores, the Japanese voted as they did from a conviction that major change is possible. Americans voted for change in 2008 in choosing Barack Obama as president, but the Japanese rejection of LDP rule in favor of the relatively young DPJ provides an interesting commentary on their assessment that, as is sometimes said in American politics, the country's best days are ahead.

Now, the new leadership is going to have a hard time bringing about the change that Mr. Hatoyama promised. The LDP consists of a well-dug-in establishment, made up of veteran government and political figures and the top management of companies and banks, comfortably in power for many decades now. They constitute the same sort of entrenched establishment in America that is made up of insurance companies, hospitals, doctors and the legislators they finance that Mr. Obama has taken on in trying to reform American health care.

The DPJ and Mr. Hatoyama have expressed the intention to change the course of the country. But to do so will present a huge challenge. The primary obstacle, as usual, will be money. Japan is heavily indebted and changes of programs will almost inevitably require injections of money. We all know the rest of that -- budget deficits, increasing expenditures on interest to service growing debt, higher taxes and, always lurking back there somewhere, the threat of inflation.

Mr. Hatoyama faces another challenge that Mr. Obama did not face. His party has little experience of governing and thus does not have a cadre of experienced public figures to call on for key positions. For better or for worse Mr. Obama had a bench full of veterans of the two Clinton administrations to call on to fill slots in his administration. Mr. Hatoyama will be required to start pretty much from scratch. His first Cabinet could look like a Pittsburgh Pirates line-up after the team's owners have just carried out one of their money-raising sales of competent players.

Another problem that Mr. Hatoyama will face is not unlike one that Mr. Obama is now encountering. He comes to office with high expectations on the part of the electorate. They got rid of the LDP and put him in office to change things that are not easy to change, to change a status quo that has strong defenders among people who benefit financially and enjoy other privileges from the present situation. Japan could quickly arrive at a point where the Japanese conclude, "Nothing has changed. This bunch are just as bad as the previous group. Woe is us."

If that were to be the case, it would be a sad state of affairs. Japan's problems are real. On the other hand, all one has to do is look at its colossal revival in the wake of the extreme economic, political and moral damage it suffered in World War II to know that the Japanese are a formidable people, not easily crushed by adversity.

The immediate impact of the election results on Japan's relationship with the United States is not clear. Mr. Hatoyama has talked about increasing the independence of Japan's posture with respect to the United States. He probably doesn't mean the trade relationship, given the importance to Japan's economy of exports to the United States. We have to hope it means no change in Japan's willingness to lend the United States money, even though its holding of U.S. debt means that its own state of economic health is highly dependent on the U.S. economy.

The U.S.-Japan defense relationship is an area of potential change. The United States continues to maintain more than 50,000 troops in Japan. But for Japan to send them home would probably mean that the cost of assuring its own defense would rise -- at a time when money will be tight.

And then there is Japan's big neighbor China, tailgating Japan economically, always a military threat and with some very bad history between the two still part of both nations' consciousness.

The good news for Mr. Hatoyama is that his party won the elections. The bad news is that now he has to govern a very complicated Japan faced with very difficult problems.