A reader poses a good question to National Review’s Ramesh Ponnuru:

An email opens up a new topic: “The United States has been the world’s greatest inspiration to freedom-lovers and young democracy movements for over 200 years. So why is it that worldwide — including now in Iraq — new democracies overwhelmingly choose the parliamentary form of government, rather than our federalist model? Is it because other nations (particularly smaller ones) don’t have the same rigid patchwork of semi-independent states we have? Or does it have to do with placating ethnic/sectarian concerns by giving them a chance to be part of a governing coalition? Still, the latter concern doesn’t seem like it would be a factor in, say, Israel.

“I have wondered this before, but I thought of it again with today’s news that Iraq has finally formed its new government. If they had followed the American model, they would have had their government in place by mid-February. The parliamentary form of government is certainly more responsive to the electorate, but its inherent instability would seem to make it a poor choice in a place like Iraq where a stronger executive branch could deal more effectively with law and order and keep things on a more consistent and even keel.

“But I’m no poli-sci expert, so please enlighten me (and maybe the Corner readers, as well).”

Ramesh then did a rare and wonderful thing — he actually asked a political scientist, who gave him a nice answer:

“Your questioner mixes two questions– parliamentarism vs. presidentialism and federalism vs. unitary states.

“Federalism has been adopted in many successful ongoing constitutional democracies, including Canada, Australia, Germany, India, and Spain.

“What hasn’t been adopted successfully is presidentialism. This is [a result of] both path dependence and selection effects.

“1a. Path dependence: Britain is parliamentary, and lots of the constitutional democracies in the world are former British colonies. Strong royal governors who existed in the 13 colonies in 1776 (standing in for a still-strong Crown at home), and strong republican governors filled their shoes, with a strong independent president following later. But by the time Canada, Australia, New Zealand, India, etc., framed their governments, their local administration and the Westminster system in London were parliamentary.

“1b. Path dependence: The [West] German Basic Law has been more influential and more widely-copied in the postwar world than has the US Constitution. And the fact that the U.S. planted parliamentary systems in Germany and Japan probably helped to kill off the thought that even the U.S. thought a separately elected strong president was necessary for constitutional democracies.

“2. Selection effects. Lots of countries have *tried* independently elected strong presidents. And they haven’t tended to remain constitutional democracies under that system. The U.S. political culture and underlying political conditions are very robustly republican-democratic-liberal; we could get a lot of institutional things wrong and still end up with a constitutional democracy. But where those things are more fragile, presidents seem to tend to become strongmen and dictators. Presidentialism has been a terrible failure in Latin America when it’s been tried– and it often was, in the 19th century, when the new Latin American republics took on the U.S. Constituion as a model.

“I’m sentimentally attached to presidentialism, and I theoretically like the stronger separation of powers you get with an independently elected executive. But the evidence suggests that the U.S. is unusual in being able to tolerate presidentialism and remain a democracy, and that parliamentarism is much the better bet for new constitutional democracies.

“(But parliamentarism is fully compatible with federalism–Canada, Australia, India, Spain.)”