一，下面这个链接是网友提供的（George Washington University 图书馆里的 Archives):

https://nsarchive.gwu.edu/briefing-book/russia-programs/2017-12-12/nato-expansion-what-gorbachev-heard-western-leaders-early

提要大概就是这几点：

The first concrete assurances by Western leaders on NATO began on January 31, 1990, West German Foreign Minister Hans-Dietrich Genscher, “NATO should rule out an ‘expansion of its territory towards the east, i.e. moving it closer to the Soviet borders.”

February 10, 1990, meeting in Moscow between Kohl and Gorbachev when the West German leader achieved Soviet assent in principle to German unification in NATO, as long as NATO did not expand to the east.

On February 6, 1990, when Genscher met with British Foreign Minister Douglas Hurd, the British record showed Genscher saying, “The Russians must have some assurance that if, for example, the Polish Government left the Warsaw Pact one day, they would not join NATO the next.”

Baker tried out the “not one inch eastward” formula with Gorbachev in the February 9, 1990, meeting. He agreed with Gorbachev’s statement in response to the assurances that “NATO expansion is unacceptable.” Baker assured Gorbachev that “neither the President nor I intend to extract any unilateral advantages from the processes that are taking place,”

上述大致是西德总理科尔和外长，美国时任国务卿贝克等，均向前苏联总统戈尔巴乔夫表达过北约不会单方面行动向东扩张。

二，北约扩张（https://en.wikipedia.org/wiki/Enlargement_of_NATO#Membership_Action_Plan)首先是要所有签约国都同意才行。它是一个开放性的集体安全防卫组织。从成立起（1949年），就有不少国家加入。比如，希腊和土耳其，然后还有西德等。

三，1994年，北约成立了所谓“合作伙伴计划”，这个计划涵盖所有前苏联包括独联体国家：

The Partnership for Peace (PfP) programme was established in 1994 and is based on individual bilateral relations between each partner country and NATO: each country may choose the extent of its participation.[168] Members include all current and former members of the Commonwealth of Independent States (From Wiki: https://en.wikipedia.org/wiki/NATO)

一度，俄罗斯也表示过加入北约的意愿。以此，北约的向东扩张，应该是没有问题了。

四，1999年，前华沙成员国波兰、捷克，斯洛伐克和匈牙利等国加入北约。2004年，立陶宛，拉脱维亚和爱沙尼亚等前苏联国家加入北约。对此，俄罗斯没有提出异议。有两点很重要：（1）立陶宛，拉脱维亚和爱沙尼亚是前苏联国家，它们的地位应该和乌克兰是一样的（虽然乌克兰被俄罗斯吞并的历史更久远）；（2）因为俄罗斯对上述国家加入北约没有异议，因此它就永久失去对其他前华沙成员国和前苏联国家（独联体）加入北约的反对权力。

结论：

某国以北约东扩，为俄罗斯普丁丁入侵乌克兰开脱的理由不能成立。