PRAGUE (AP) — Reaching anew for peace, President Barack Obama and Russian President Dmitry Medvedev on Thursday signed a treaty to shrink their nations’ nuclear arsenals, the biggest such pact between the former Cold War foes in a generation.

Tenaciously negotiated by even the leaders themselves, the treaty commits their nations to slash the number of strategic nuclear warheads by one-third and more than halve the number of missiles, submarines and bombers carrying them.

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In a lavish chamber within the Czech capital’s presidential castle complex, the two presidents put their names to history. The treaty must be now be ratified by Russia’s parliament and by the U.S. Senate, where the White House lobbying effort is under way.

The new treaty will shrink the limit of nuclear warheads to 1,550 per country over seven years. That still allows for mutual destruction several times over. But it is intended to send a strong signal that Russia and the U.S. — which between them own more than 90 percent of the world’s nuclear weapons — are serious about disarmament.