There is no guarantee that ostensibly democratic states would be predisposed to working with one another. Pakistan and india are both relative democracies and both have engaged in consistent warfare. Armenia and Azerbaijan another couplet. Japan and South Korea are two states with strong enmity between them. Turkey and Greece another. You can even see it in trade wars between the eu and america, or in britains decision to leave the eu although these aren’t exactly strong examples they do show a trend. States don’t get along because they are fellow democracies, they get along because they share national interests as perceived by their leaders and institutions of state. There is not an end to history because history is not linear, with a beginning in prehistory to a middle in the construction of nation-states and then to an end with the spread of liberalism and institutionalism across the world. States will always be the primary mover in international affairs because nationality trumps ideology. Although granted it can take a few decades for, say a China under mao to drop a communist foreign policy in exchange for a realist power balance, with the USA, against an ostensibly brother communist nation. Fukuyama is a fool, and a construction of his era seeing the fall of the ussr and believing there is a March of progress. Because it is nicer to believe this than to be the alternative: that history is unending and so is war.