A political showdown looms in Hong Kong. Beijing has stripped the city of the high degree of autonomy it promised in a 1984 treaty with the United Kingdom. Local residents are preparing a campaign of civil disobedience in protest. Yet London has failed to express even mild criticism of Beijing's treaty violation.

The people of Hong Kong overwhelmingly want to elect their next Chief Executive, a reform that until a month ago seemed within reach. On Monday university and secondary students began a week-long boycott of classes...