The fact that in the twentieth century a greater proportion of the people in the world could communicate with one another, using English or just a few other languages, appears not to have stopped any wars, nor to have reduced the frequency with which wars have broken out, nor to have made the wars that have broken out less brutal. In fact, several murderous wars have been fought recently among people who speak 'the same language' in real terms.
Andrew Dalby, Language in Danger: The Loss of Linguistic Diversity and the Threat to Our Future
language, war