The last US-Russian nuclear pact is about to expire, ending a half-century of arms control

Russia US Nuclear Treaty - (Copyright 2010 The Associated Press. All rights reserved.)

The last remaining nuclear arms pact between Russia and the United States is set to expire Thursday, removing any caps on the two largest atomic arsenals for the first time in more than a half-century.

The termination of the New START Treaty would set the stage for what many fear could be an unconstrained nuclear arms race.