The emergence of democratic constitutions: comparing the modern world to ancient Greece
比较古希腊城邦与现代国家两个世纪的数据，发现民主在两者中均因转型频繁而逐渐成为主流，但古希腊民主比例曾多次波动，现代世界刚达50%门槛，后续是否重演希腊模式尚待观察。
Abstract Democracy has flourished twice in human history: first in ancient Greece and then, more than two millennia later, in the modern world. Although the historical record regarding most Greek poleis (city-states) is scant, there nevertheless exists sufficient information to categorize the constitutions of nearly 200 of the more than 1000 poleis that once existed. Using similar data from the modern world, we compare two centuries of ancient data to two centuries of modern data. In both eras, democracy grew in prevalence because, over many decades, transitions to democracy were sufficiently frequent to offset “backsliding” away from democracy. Thus, democracy eventually became the most common form of constitution in both ancient Greece and the modern world. Democracy appears to have expanded more rapidly among Greek poleis than among modern countries; however, we observe that after reaching 50 percent, the proportion of Greek democracies declined, rose again to half of all states, declined again, and rose to half again. The modern world just recently reached the 50 percent threshold, and whether it follows the Greek pattern remains to be seen.