Revolutions, it is often claimed, do not happen when people are desperate. They occur in times of rising expectations. Perhaps this is why they so often end in disappointment. Expectations, usually set too high to begin with, fail to be met, resulting in anger, disillusion, and often in acts of terrifying violence.

Japan's change of government in 2009 – when the Democratic Party of Japan (DPJ) broke the almost uninterrupted monopoly on power held by the Liberal Democratic party (LDP) since 1955 – was not a revolution. But, rather like the election of the first black president of the United States, it was fizzing with popular expectations, promising a fundamental shift from the past.

This was even truer of Japan than the US. The DPJ not only put many new faces into power, it was going to change the nature of Japanese politics. At last, Japan would become a fully functioning democracy, and not a de facto one-party state run by bureaucrats.

To judge from the Japanese press, as well as the DPJ's plunging poll ratings, disillusion has already set in. The permanent bureaucracy proved resistant, and DPJ politicians, unused to power, made mistakes. One of the worst was the June announcement by the prime minister, Naoto Kan, of a consumption tax hike just before the upper house elections, which the DPJ went on to lose badly.

The other disappointment has been the government's failure to get the US to move its Marine airbase out of Okinawa. This promise by the DPJ was meant to be part of Japan's new assertiveness, a first step away from being a mere "aircraft carrier" for the US, as a former LDP prime minister once described his country.

If Japan's status quo is to change, the country's oddly skewed relationship with the US is one key factor. Too much dependence on American power has warped the development of Japanese democracy in ways that are not always sufficiently recognised by the US.

Japan's one-party state, under the conservative LDP, was a product of the second world war and the cold war. Like Italy, its old Axis partner during the war, Japan became a frontline state in the battle against communist powers. And, as in Italy, a rightwing party, backed by the US, dominated politics for decades in order to crush any chance for the left to take power. Even former Japanese war criminals, one of whom became prime minister in the late 1950s, became subservient allies of the US in the wars (hot and cold) against communism.

In fact, Japanese dependence on the US was even greater than that of Italy and other European powers. West European armies were embedded in Nato. Japan, whose armed forces were entirely blamed for driving the country into the catastrophic Pacific war, was not even supposed to have an army or navy after the war. During their occupation of Japan in the 1940s, Americans wrote a new pacifist constitution, which made the use of Japanese military force abroad unconstitutional. In matters of war and peace, Japan abdicated its sovereignty.

Most Japanese were happy to be pacifists and concentrate on making money. Japanese governments could devote their energy to building up the country's industrial wealth, while the US took care of security, and by extension much of Japan's foreign policy. It was an arrangement that suited everyone: the Japanese became rich, the Americans had a compliant anti-communist vassal state, and other Asians, even Communist China, preferred Pax Americana to a revival of Japanese military clout.

But there was a steep political price to pay. A democracy that is over-dependent on an outside power, and monopolised by one party whose main role is to broker deals between big business and the bureaucracy, will become stunted and corrupt.

Italy, under the Christian Democrats, had the same problem. But the end of the cold war in Europe changed the political status quo – with mixed results, to be sure. Old parties lost power, which was a good thing. The vacuum was filled in Italy by the rise of Silvio Berlusconi, which may have been less of a good thing. In east Asia, by contrast, the cold war is not yet entirely over. North Korea still causes trouble, and China is nominally a communist state.

But it is a very different world from the one left in ruins in 1945. For one thing, China has become a great power, and Japan, like other Asian countries, must adapt to new circumstances. But, while it is the only Asian democracy able to balance the power of China, the system established after the second world war is not best suited to this task.

This was recognised by the DPJ, which would like Japan to play a more independent role, as a more equal ally, rather than a mere protectorate, of the US, and thus be a more assertive political player in Asia. Hence, the first symbolic step was to get the US to move its marines from Okinawa, an island that has carried the burden of a US military presence for much too long.

The US did not see things that way. The DPJ threatened to change comfortable old arrangements, whereby the US could more or less tell the Japanese what to do. As a result, the US showed little patience with Japan on the question of Okinawa, and has barely concealed its contempt for the DPJ government, feeding popular disappointment with its performance so far.

The US seems to prefer an obedient one-party state to a difficult, faltering, but more democratic partner in Asia. The Obama administration, struggling to fulfil its own promises of change, should be more understanding of its Japanese counterpart. If the US is as serious about promoting freedom abroad as it claims, it should not be hindering one of its closest ally's efforts to strengthen its democracy.

• Copyright: Project Syndicate, 2010.

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