Democracy protects against war?

It is sometimes stated that two democracies have never gone to war. If true now and in the future, the world would have no wars if all countries were democracies.

One trouble with the step from democracies have never fought each other to democracies will never fight each other is that the sample set of democracies in the past were mainly Western European and North American, who had little incentive to fight and were closely tied in other ways too. So the second hypothesis may not apply outside these countries.

I am not sure whether the democracies have never fought each other assertion is true in the past, not having information about all conflicts. There have been two recent conflicts, one in the Middle East and now one in the Caucasus, where democracies seem to have fought each other. There are questions about how democratic the parties involved were, but all the same, it doesn't seem that mutual democracy is a perfect protection against conflict.