Except for the War of 1812, (1) the First World War (hello, Reichstag), (2) the Second World War (hello, Finland), (3) the American Revolutionary War, (4) the Fourth Anglo-Dutch War, (5) the Belgian Revolution, (6) the American Civil War, (7) the Spanish-American War, (8) the First Boer War, (9) the Second Boer War, (10) the Polish-Lithuanian War of 1920, (11) the British invasion of Iceland (also in WW2), (12) the Football War, (13) the Israeli-Lebanon War (of 2006), (14) and the Russo-Georgian War of 2008... (15) And I'm sure I've missed a few. (16)
Democracies don't war with one another... except when they are not democracies. (17)
1) The pre-1832/1867 British were not a democracy
2) The Germans in WWI were ruled by a military-dominated monarchy. Goodbye Reichstag.
3) The Finns were invaded by a Communist Soviet Union, and then in turn attacked them after Barbarossa. Having made their bed, the Western Allies declared war on them only on Soviet insistence.
4) See (1) about the British. With a fully truly representative Parliament and a king stripped of his powers the Loyal Opposition of the time could easily have been elected and gained a peaceful settlement long before the first shots were fired.
5) See (1). Call Britain of the time an oligarchical constitutional monarchy if you like, but it was no democracy.
6) The monarchy ruling the United Netherlands was not a democracy. The Belgians were not being democratically represented.
7) The Confederacy was not a democracy. There were no referendums on Secession, and any dissent against it by the 20% of the White population who were Unionist (and that's not even counting the Border States that the Confederacy claimed as their own) was brutally, even bloodily, suppressed.
8) Probably the closest possible example you've provided, even with the corrupt turno system in which the Spanish King CHOSE the government to be elected, and then the "election" assured it. I guess I should've dis-included "banana republic/constitutional monarchies".
9) The Boers were no more a democracy than Apartheid South Africa
10) See (9) It doesn't excuse British avarice, however.
11) NEITHER country had a democratic tradition, had only just immediately come out of occupation by dominating non-democratic powers that very year, were both fighting wars on multiple fronts against Germans, Soviets, indigenous forces, and each other. Despite all that, as two very newborn republics they tried to hammer out a peace agreement between each other. Tried, and succeeded. Only to see it fail thanks to rebellious military officers. Not an unusual problem to be faced in the inter-war period in Eastern Europe. And both Poland and Lithuania would fall into military dictatorships in all but name in 1926 anyway.
12) THAT was a peaceful occupation in fear of German aggression. Iceland doesn't even HAVE a military!
13) Banana republics are not fully functioning democracies, and it lasted all of 100 hours
14) Hezbollah is not a democracy
15) You would describe Putin's Russia today as a democracy?
16) And I stand by my statement that democracies do not war with one another. You have a VERY generous concept/definition of what constitutes a "democracy". Do perchance you include the Ancient Roman Republic and the Greek City States too?
17) Fixed it for you
Apologies for going off point