Twenty-six years after the Islamic Revolution, just when the West had expected Iran to settle down and become more pragmatic, the regime of President Mahmoud Ahmadinejad seems to have lurched back toward radicalism. By looking at earlier revolutions, we can perhaps come to understand what is happening in Iran, for recent events there have clear historical precedents.

Many revolutions have passed through an initial “quiet” period after an early phase of radicalism, only to experience a resurgence of radicalism 15-25 years later. This is because the initial quiet period is often marked by corruption and a retreat from revolutionary goals, leading idealists to feel that the revolution is losing its way. Believing that stronger pursuit of revolutionary ideals is the only way to strengthen their country, these idealists seek to inspire a “return of the radicals,” triggering sharp conflict with their more pragmatic co-revolutionaries.

The Mexican Revolution of 1910 began with a challenge to the dictator Porfirio Díaz that ignited peasant uprisings and worker revolts. The revolution’s radical phase seemed to end in 1920 when General Alvaro Obregón seized power; he limited land reforms and sought reconciliation with the United States. For the next 14 years, Obregón and his ally General Plutarco Calles ruled Mexico.

Then, in 1934, resentment against growing corruption led Calles to choose an “honest idealist” to become president, a young man who had fought for him early in the revolution, who he thought he could control but who would help the government regain popularity. That “honest revolutionary,” Lázaro Cárdenas, toured the country, building his popular support, and then turned on Calles, expelling him from Mexico.

Known for both his radicalism and his honesty, Cárdenas refused to live in the presidential palace and cut his salary in half. He also took seriously the early goals of the revolution, embarking on massive land reforms. In 1938 – twenty-eight years after the revolution began – Cárdenas provoked a major confrontation with the US and Britain by expropriating their oil companies and nationalizing Mexico’s petroleum. Only in the 1940’s, after Cárdenas left power, did Mexico turn to a more conservative political path.

Similarly, China’s Communist Revolution began with a decade of attacks on the middle and professional classes and a reshaping of the countryside, culminating in the Great Leap Forward of 1958-59. But that disastrous campaign weakened Mao’s influence; by the early 1960’s he seemed to be relegated to the sidelines while pragmatists like Liu Shaoqi and Deng Xiaoping grew stronger.

Yet Mao worried that his revolution was going off track, and in the mid-1960’s he launched an effort to regain control of the Party by educating a new generation of radical youth. These “Red Guards” launched the Cultural Revolution in 1966-68, targeting the more conservative elements within the Communist Party. The Cultural Revolution tore China apart, but it returned Mao to supreme power and allowed him to purge the pragmatists.

But did the battle between pragmatists and radicals end there? In the early 1970’s, moderates gained by engineering a rapprochement with the US, capped by Nixon’s famous visit to China in 1972. Deng was rehabilitated the following year, and in the late 1970’s, after Mao’s death, Deng’s pragmatists seized control of the regime.

What do these historical examples suggest for Iran? It is likely that the relatively calm period dating from Khomeini’s death in 1989 is over. The election of Ahmadinejad marks the onset of new struggles within the ruling Islamic Republican Party. These pit the “honest radicals”- led by Ahmadinejad and supported by younger, second-generation revolutionaries known as the Abadgaran, or Developers, who are strong in the Iranian parliament, the Majlis- against the more corrupt and pragmatic mullahs who head the Party, led by Expediency Council Chairman and former President Hashemi Rafsanjani. Supreme Leader Ayatollah Khamenei is left in the middle, perhaps increasingly isolated and without strong popular support.

How should the US and European leaders respond? Historically, phases of resurgent radicalism have lasted 5-10 years, marked by greater aggressiveness against internal and external enemies.

This bodes ill for improved relations with Iran in the short run, and makes it imperative that Western powers unite to make it unambiguously clear that any use of nuclear weapons or materials by Iran or terror groups aligned with Iran will result in an immediate and devastating response. (China developed its nuclear weapons just before its Cultural Revolution, mainly to deter the Soviet Union, but never used them).

It also seems advisable to offer positive incentives – including US recognition and an end to sanctions – that could help empower pragmatists in their intra-Party struggle, much as Nixon’s overtures to China helped blunt China’s radicalism and strengthened the hand of pragmatists in the Communist Party.

Nixon did not demand that China’s leaders abandon communism or that Mexico become a competitive democracy, only that they act responsibly and learn to do business with the US. Five decades after its revolution, China is still not a democracy, and Mexico is only just becoming one nine decades after its revolution. Neither country always sees eye to eye with the West. But both became countries with which it is possible to do a great deal of business, and both are increasingly integrated into the global economy. That may be the only realistic goal in dealing with Iran.