Historical clue formulations

• First of two U.S./U.S.S.R. pacts — 2019-12-29
• Nixon and Brezhnev signed it in '72 — 2015-06-19
• Pact signed by Nixon — 2015-02-21
• 1970s pact partly negotiated in Helsinki — 2013-11-01
• 1972 missile pact — 2011-05-12
• 1972 U.S./U.S.S.R. pact — 2009-08-07
• 1972 U.S./U.S.S.R. missile pact — 2007-10-22