One reason is that the Obama administration is rethinking a planned missile-defence system, which would have placed ten interceptor rockets in Poland and a radar station in the Czech Republic, in order to guard against Iranian missile attacks on America and much of Europe.
It is the only place on earth where, under the anti-ballistic missile treaty, the United States was allowed to test its strategic interceptor missiles, a key component of President Bush's missile-defence programme, sometimes known as Star Wars II.