Some pre-modern empires ruled an extraordinary variety of peoples. When they managed to do so for quite a long time (though no empire lasted for ever), they mostly left local customs, languages, and so forth alone, content with making local rulers their vassals and merely collecting tributes from their peoples indirectly.
Since the rise of modern nationalism, local customs, languages, and so forth have often become "problems" for nation states, for nationalists have often demanded homogeneity in such matters, on top of the fact that capitalism tends to favor standardization (e.g., about conceptions of time, orthographic rules, etc.).
Modern capitalist empires tend to exacerbate national questions, for they opportunistically support states (e.g., the Philippines government) against sub-state nationalists (e.g., Muslim separatists in the Philippines) who are official enemies or sub-state nationalists (e.g., Arabs in Khuzestan province of Iran) against states (e.g., the Iranian government) whose power elites are official enemies, according to their ever-changing geopolitical agendas.
-- Yoshie <http://montages.blogspot.com/> <http://mrzine.org> <http://monthlyreview.org/>