The debate over NATO after the collapse of the Soviet Union was extensive but ultimately came down to that NATO had been a success that ought not to be discarded until Russia's ultimate direction and attitude toward the US and Europe had become clear.
As it was, post-Soviet Russia's economic and political chaos led to the near dissolution of its military for lack of funding. NATO military spending also declined due to a lack of apparent need. In effect, NATO had become almost a dead letter until 9/11 and Putin's rise.
Ukraine was persuaded to give up its nuclear weapons inherited from the Soviet era in return for security guarantees from the US, NATO, and Russia. As it was, those guarantees proved useless when Putin came to power.
My understanding of the Balkans war is that Serbia was the aggressor. The Serbs had dominated the artificial amalgamation of nationalities and cultures that was Yugoslavia and wanted to recover control over them, especially against Muslims resident in areas that were geographically and historically significant to Serbia. The shorthand for this was that they wanted to build greater Serbia.
Similarly, Putin aims at the building of a modern Russia that would dominate her immediate neighbors like Ukraine and intimidate NATO and historical opponents like Poland and the Baltic republics and the Nordic countries. In Putin's plan, Germany was to be bought off through cheap oil and gas.
Putin wanted control of Ukraine but the Ukrainians mostly did not want to be had by Russia. Poland and Great Britain -- genuine and essential US allies in Europe -- support Ukraine as a buffer against Russia.
Where we come close to agreement is on the catastrophic effects of mass immigration. The Europe of today and European civilization itself are dissolving away under its impact, with the US and Canada also in grave danger. Soviet Communism failed, but the Left may yet destroy Europe, the US, and Canada through mass immigration.
From that perspective, my support for Ukraine is a matter of national security strategy against Russia and Putin. The larger problem of uncontrolled mass immigration remains. And if feeding Ukraine to Russia would solve that, you and I would have little to disagrre about.
Serbia was not the aggressor. There are far larger things at play, but I can tell you won’t be and to have your worldview challenged to that extent.