Since we're into history here in this thread, maybe my perspective will add some depth to this particular conversation. It may also bring some depth to discussion around how best to respond in Ukraine.
TL;DR - some types of pacifism aren't the same as passive-ism - creating peaceful relationships requires hard work. War is a failure to love our fellow humans, to deal with conflict before it gets out of control, and from turning a blind eye to injustice. By the time war breaks out it is inevitable, we have failed to take advantage of the myriad opportunities we had along the way to work for peace...
I am a pacifist, but not a passivist (this isn't a mainstream distinction, but one made in my circles). I'm a Mennonite, but not the old-colony kind with horses and buggies - I drive a Tesla and don't have religious rules around clothing. There are a diversity of beliefs within this theological stream - some are more passive and avoidant, others are more active and work for reconciliation. Just being anti-war is meaningless - to just be against something; you need to be "for" something to do anything meaningful.
I try to actively work for peace (not the absence of conflict, but a life characterized by healthy relationships between others - starting with family and neighbours, and then as I can with acquaintances and politically - similar to the Jewish shalom concept). That means starting with learning how to communicate non-violently (hard to do); not viewing differing viewpoints as scary/evil, but as learning from others and helping others learn. Conflict is inevitable, but the goal is to not break relationships because of it - though it takes wisdom to recognize when people need to be cut off to avoid enabling their destructive behaviours. But if we fail, we have to leave behind idealism and figure out what to do with the mess, and there are no easy answers - suffering is inevitable, no matter one's choices at that point. Bonhoeffer's autobiography was enlightening for me personally - diplomacy didn't fail because Germans were all evil, but the failure of nations to pursue reconciliation created a victim mentality and disenfranchisement that led to populist fascism. But back to my history (to do Bonhoeffer justice, I'd have to write 10 paragraphs to scratch the surface).
My ancestors came from the Netherlands, and were burned at the stake and tortured by both Protestants and Catholics post-Reformation because our beliefs were an existential threat to Christendom and theocratic politics: by rebaptizing adults instead of recognizing infant baptism, they stated that one's life should reflect Jesus' teachings (like loving even your enemies - which incidentally doesn't mean enabling them or letting them do whatever they want, but refusing to dehumanize people - but I'll try to avoid a theological rabbit hole...). You're not at automatic Christian - Christianity should be trying to imitate the way Jesus treated others; most politicians and priests didn't bother... The concept of loving enemies, living simply and sustainably, being free to choose one's religious beliefs, not blindly following political on religious leaders (but allowing churches to split off rather than forcing uniformity by killing those you disagree with) were all scary concepts to those in power back then.
Due to the persecution, we first fled to Prussia, then were invited by Catherine the Great to develop an area near the Black Sea in the early 1800's - my particular ancestors lived in the
Molotschna colony. In the 1870's my ancestors were among the first to notice changes in the government's attitude, and so we left peacefully and settled in Canada where we were promised peace.
Some have heard of the Mennonite Central Committee - an international organization that started during the early 1900's to help those Mennonites who had stayed in Russia/Ukraine to escape the rising violence and government takeovers. The rise of Communism was particularly hard on those who stayed, and the Mennonites were essentially wiped out (they suffered under the artificial famine - the gov't took their harvest, leaving nothing for the farmers, and WW2 took care of the rest). The MCC helped Mennonites move to Canada & the USA - it was even worse when the Communists took over; constant looting and many were imprisoned in Siberia. The last ones fled with nothing but the clothes on their backs.
MCC has grown to help other culture groups suffering across the world - sending grain and clothing to those who have nothing, and training locals to produce food or goods in more sustainable ways. An arm of MCC is the Mennonite Disaster Service (MDS) - they send out tradesmen to help the poor rebuild their homes after disasters, like Hurricanes down South. Another local cause I personally support a lot is an organization that mentors kids in the downtown area of Winnipeg, mostly First Nations but also the poorest of the poor. It's a drop-in centre that includes teaching trades and giving kids a safe place to eat and hang out and avoid gangs and violence. This is an amazing example of pacifism - replacing weapons with tools.
The idea is that by helping the poor and the downtrodden, easing suffering, treating humans from different cultures with love and generosity, we build bridges and friendship. Training helps people become self-sufficient and avoids a victim or refugee mentality.
Sometimes this is taken advantage of, and it's a hard line to walk. We left many places because staying would enable the abusive relationship: when the government is corrupt and gets to the point of removing rights and killing peaceful citizens, if you choose to fight their way you will lose, so leaving means they lose productivity, valuable citizens and people to bully. Like today, the Russian gov't only knows how to take, not produce. If peaceful, productive people leave, there is nothing left to steal. But in the short term, it seems as though that gives the powerful dictators a win. Mennonites used to avoid politics, and that was a mistake - being Quiet in the Land helped them have peace with their neighbours, but not with corrupt governments. So we're learning to become better at speaking out. Treating political opponents as humans goes a long way - the second we start killing enemies, they now feel justified that they are correct, and will feel no remorse at killing us back. But to kill a human who has been kind to you, who treats others well, who actively helps you - that creates a cognitive dissonance. It starts with language, but actions are also key. It starts at the individual level, and extends outwards from there.
As far as military goes, I don't blame anyone for fighting. It's the most direct solution, though it's not sustainable in the long run, and causes trauma and harm to both sides. I think there's an issue if anyone glorifies it or enjoys killing, but most people don't; both sides do it because they believe they have no choice and are justified (or at least they believe it benefits them or they have an obligation). And I think there comes a point where war is inevitable, if we have failed again and again to deal with injustices and poverty, and have created victims by our peacetime actions.
Right now, Ukraine Russia is obviously past the point of peace, and the world's failures to deal with Putin (turning a blind eye because it profited our politicians, and actually enabling his government's corruption by accepting bribes and influence-peddling) means democratic governments are forced to support a war now.