The central concern to many Europeans is whether such a proposed venture would be in breach of existing nuclear treaties. The 1972 anti-ballistic missile treaty, signed by the United States and Russia, forbids the development of a nationwide defence system. Should the U.S. proceed, it would either need the agreement of Russia to amend the treaty or it would have to unilaterally reject the treaty. Talks between Washington and Moscow have begun, but so far Russia appears firmly opposed to anything which it believes might weaken the effectiveness of its nuclear deterrent. There are also American proposals to install radar and communication installations in Greenland, technically under the sovereignty of Denmark.
European countries appear to hold substantial reservations about the program.
Short of England which has been a traditional ally of the U.S., most are concerned worried about the U.S. pursuing a unilateral defence policy, and thus, provoking Russia. There is also concern that a defensive screen for the U.S. alone would leave the Europeans vulnerable. Washington has begun discussing a regional defence system. However, the Americans have yet to win the support of their Nato partners. The Chinese have warned that they might be forced to boost their own military deployments if the system is given to South Korea, Japan or Taiwan.