As Russia masses troops along its border with Ukraine, American policy makers are mulling what action to take to deter Moscow from invading its neighbor. Options have ranged from troop deployments to supporting a Ukrainian insurgency like the Reagan in Afghanistan during the 1980's. Both options will inevitably involve American defense and intelligence personnel along with taxpayer money that can be better used elsewhere. The libertarian position would be to avoid any military involvement against Russia. Such participation would violate the LP's non-aggression principle while also helping to destabilize another region that can fall victim to the proliferation of violent substate groups in the absence of a stable government. Though the Kremlin engages in policies that libertarians find appalling, a conflict in Ukraine does not directly threaten the United States rendering American involvement unwarranted.
Stating the non-aggression principle isn't enough. As libertarians find themselves climbing the ranks of government, we will inevitably find ourselves in positions that impact foreign policy. Not only would American support of Kyiv against Russia violate libertarian values, it's also just plain bad geopolitics.
Two things to consider about Russia are its internal politics and its geography.
Firstly, Russia consists of a large, thinly populated landmass with few geographic barriers to protect it. Historically, the Kremlin has maintained a policy of defense through outward pressure. This means that to prevent an adversary from massing an invasion force on one of its borders, Moscow wants to keep its neighbors either unstable or preferably in some form of vassalage or subservience. Given that Ukraine has historically been either a part of Russia or at least in its sphere of influence, it makes sense that the Kremlin would want to control that space.
Secondly, Putin's internal control of Russia is not as strong as many in the West tend to think. His power comes from a coalition of oligarchs, government agencies, and criminal organizations that receive Kremlin support for helping to maintain order. Over the past few years, this coalition and Putin's popularity have waned. To stay in power, it's not uncommon for leaders to try and redirect domestic frustration towards existential threats to get people to cooperate by rallying them to a patriotic cause. Given the large population of Slavs in Ukraine and Russia's self-appointed role as their defenders, a war in Ukraine can be just that patriotic cause.
Now let's take a step away from Russia's geography for a moment and look at the end of the Cold War.
After the fall of the Soviet Union, Washington promised Moscow that it would not expand NATO to include former members of the Warsaw Pact. Afterall, NATO was formed specifically as a deterrent to the USSR, which no longer existed. Furthermore, Russia was to join the West as a free market economy.
Unfortunately, the newly formed Russian Federation fell into an economic depression that witnessed a general decline in living standards. NATO also pushed eastward and even inducted former Warsaw Pact members like the Czech Republic, Hungary, and Poland to name a few. Many Russians resent the way that the Clinton Administration seemingly walked over Boris Yeitsin in the immediate aftermath of the Cold War, which has become a useful propaganda tool.
Back to the present. Viadimir Putin wants to rebuild a Russian Empire and restore his country's international influence and prestige. Russia's local defense depends on a policy of outward pressure and its internal politics need an existential boogey man to keep disgruntled citizens at bay. American involvement in a war between Russia and Ukraine will give Putin the propaganda talking points that he needs. Meddling in local Russian affairs would invite the same in the United States and the Western Hemisphere (though this isn't to say such meddling should be ignored either but should be met in kind). Furthermore, reckless interference in Russia's sphere of influence can escalate into a broader multi-domain conflict with a nuclear armed near-peer adversary. With Americans occupied in Eastern Europe and likely polarized further at home, China will be more emboldened to challenge a distracted and over extended United States in the Pacific.
Libertarians can empathize with the Ukrainian people. They're in a tough spot with a nasty adversary. Unfortunately for them, this isn't America's fight.