 The pact replaces the 1991 Strategic Arms Reduction Treaty (START I), which was signed by U.S. President George H.W. Bush and Soviet President Mikhail Gorbachev in the final days of the Soviet Union . START I expired in December of last year.
<clarity>  The pact replaces the 1991 Strategic Arms Reduction Treaty (START I), which was signed by U.S. President George H.W. Bush and Soviet President Mikhail Gorbachev in the final days of the Soviet Union . START I expired in December of last year.
 The pact replaces the 1991 (START I), which was signed by U.S. President George H.W. Bush and Soviet President Mikhail Gorbachev in the final days of the Soviet Union . START I expired in December of last year.