Unanswered questions abound over the United States' missile defence system. While its reasoning remains unclear, China, Russia and North Korea have as much right to increase military defences as the US does in constructing and deploying so threatening a network of missiles. President George W. Bush's avowed self-defence system is far from complete and will be put in place as it is developed. It flies in the face of international agreements on non-proliferation of weapons. He can hardly be surprised that China is developing better and longer-range missiles or that North Korea is threatening to restart testing programmes. The US sees itself as the protector of world peace, but it cannot see that its actions are having the reverse effect. President Bush's plan announced on Tuesday calls for 10 ground-based interceptor missiles in Alaska by 2004 and an additional 10 by 2005 or 2006. The US has correctly called North Korea a rogue state. Pyongyang's secret acquisition of a plutonium enrichment programme and ignoring of an agreement to mothball its ageing nuclear power facilities point plainly to the danger it poses. Although it has developed and test-fired a medium-range missile, it is not believed to have weapons capable of hitting the mainland US. China and Russia do. With more than 700 inter-continental ballistic missiles, Russia could easily fire a volley at the US which would overwhelm its interceptor system. China is believed to have 20 long-range missiles - enough exactly for the missile shield to cope with. The argument could easily be put, therefore, that Washington's system is being rushed into action to cope with a threat not from Pyongyang, but from Beijing. Political pundits would prefer to think that Mr Bush's bid for re-election in 2004 is more likely the reason. But given the desire to rush into place a system that has so far proven to be technically flawed, it would also be seen as a warning. Mr Bush should realise that while he seems intent on weapons proliferation, his actions are being seen on this side of the Pacific as a green light to follow by example in the name of self-defence.