Sure. But you can come up with equally plausible standards that cut the other way: for instance, Germany had achieved universal male suffrage while Britain still had property requirements and was much more vigorously fighting women's suffrage with state repression. The German High Command could mobilize troops and declare war without parliamentary approval, but, hell, we effectively allow that in the USA today. And it's not like the German populace were snookered into the war: the Reichstag was not only willing but ecstatic to vote to support and fund the war. It's not the case that every German was happy about the war, but response was akin to the American national rallying that happened after 9/11.

I wouldn't want this to become a tit for tat about who was the real democracy in the war: I'm perfectly happy to say that every participant fell far short of democracy. But the democratic peace folks are making a seemingly predictive, scientific claim using a really fuzzy and emotionally laden term like democracy that's easy to bend to mean whatever you like.

If there's something that's meant beyond my "US/UK and their allies don't fight each other" idea, I'm all for hearing it out. What are some of the countries considered democracies by the democratic peace proponents that aren't in that alliance and seem not to have been in a war with that alliance due to the fact that they're democratic and not autocratic?

I do concede that there it isn't inherently an error to say one country is more democratic than another, and that the Ottomans and Austria Hungary clearly end up on the losing side of that comparison.

One argument you might make is that the democracy peace theory is really just the Anglosphere. As Bismarck put it, "never underestimate the fact that Britain and America speak the same language."

You wouldn't imagine a civil war amongst a homogenous culture. I wonder if the Parliamentarians/Royalists or the Unionists/Confederates were more culturally different than the Anglosphere cultures are today.

I'm not quite up to speed on how bad the UK's and US's electoral systems were at the time, but a lot of the British Empire had universal suffrage, e.g. AU, NZ.

Germany had tiered suffrage until the 1918 revolution.

"This distribution meant that a first-class vote had 17.5 times the value of a third-class vote." and "... one result of which was that the industrialist Alfred Krupp was the only person able to vote for the electors in the first class in Essen."

http://en.wikipedia.org/wiki/Prussian_three-class_franchise

Germany had a different electoral system (one that included equal, universal suffrage) than Prussia, which was at a different, lower level than Germany.