For now, the response of the United States and its allies will be confined to public statements and diplomatic protests. But the longer-term reaction in terms of threat perceptions and the technological and spending answers to them will be crucial and could be huge. Meanwhile, the missile event will not make it any easier for the United States and China to find a way out of tensions arising from their huge trade imbalance.
In a narrow sense, China had every right to use one of its own rockets to destroy its own obsolete satellites. Beijing could argue that it was exercising its own right to unilateral action to protect its national interests in the same way that the United States has so often done during the Bush administration. The United States itself once destroyed old satellites and in August reiterated its opposition to a formal ban on space weaponry or on any restrictions on its space activities.
But that is not the point. In the first place, China's action offends against the informal international understanding that had long existed to desist from sending weapons into space, and to avoiding filling space with the debris of exploded satellites that could put other satellites out of action.