although not a single event, for the 19th century I would add emergence of nationalism in the Western world in the modern sense of the term, i.e. the strong feeling of identity binding together communities of peopl,e surpassing social, confessional or other differences among them. there were many "nationalistic" notions before modern period but there were to some extent always dependent on some special conditions and thus limited to special group of society... but since the 19th century nattionalism became a "mass movement" and has influenced the course of history sinbce. it seems to me that nowadays people (in Europe at least) can barely view the world without taking it into account.