It was only a little more than a decade ago that a country first legalized same-sex marriage, and that happened in precisely the kind of forward-thinking, bohemian place you'd expect: the Netherlands. About two years later, Belgium followed suit.

Then things got really interesting. The eight countries that later joined the club were a mix of largely foreseeable and less predictable additions. In the first category I'd put Canada, Norway, Sweden and Iceland. In the second: South Africa, Spain, Portugal and Argentina.

Why those four countries? People who have studied the issue note that that they have something interesting and relevant in common: each spent a significant period of the late 20th century governed by a dictatorship or brutally discriminatory government, and each emerged from that determined to exhibit a modernity and concern for human rights that put the past to rest.