Earlier quoted context omitted.
Because despite agreements to the contrary, NATO keeps trying to expand into Ukraine.
What agreement? This is the agreement that Russia signed to guarantee the integrity of Ukraine: https://en.wikipedia.org/wiki/Budapest_Memorandum_on_Securit... What agreement did NATO sign to not expand? Produce it!
"President Bush also assured Gorbachev during their meeting in Malta in December, 1989, that if the countries of Eastern Europe were allowed to choose their future orientation by democratic processes, the United States would not “take advantage” of that process. (Obviously, bringing countries into NATO that were then in the Warsaw Pact would be “taking advantage.”) The following year, Gorbachev was assured, though not in a formal treaty, that if a unified Germany was allowed to remain in NATO, there would be no movement of NATO jurisdiction to the east, “not one inch.”"