Ethnic Russians were seen as a means to reverse the empire's contraction all the way back in 1992:
Mr. Karaganov hypothesized two decades ago that the Russian speakers living in newly independent countries such as Ukraine, Belarus and the Baltic states would become the prime guarantors of Moscow’s political and economic influence over its neighbours after the fall of the Soviet Union. In a 1992 speech that laid out what became known as the “Karaganov doctrine,” he prophesied that Moscow might one day feel compelled to use force to protect them, and thus its interests, in the former USSR.
Putin didn't adopt this doctrine back then. But the impulse was there waiting for Putin to harness it as Russia recovered some power. Defeat in the Cold War prompted this thinking and not any particular Western action after the events of 1989-1991.
