You have the right to be wrong.
Here's a good definition for environmentalism. Compare and contrast it to your definition of militarism:
Environmentalism
Political ideology
Environmentalism or environmental rights is a broad philosophy, ideology, and social movement regarding concerns for environmental protection and improvement of the health of the environment ...
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For the sake of discussion, I'll use your definition for the Russo-Ukraine war:
Ukraine is said to have been attacked by Russia without provocation. Therefore, according to your definition, the only choice that Ukraine has is to engage in war. For the sake of discussion, I'll accept both of those statements as being true and complete.
So, we'll go with "Ukraine must war with Russia."
Now, does everyone else that is participating in the Ukraine defense effort have no other choice? Does the US have no choice but to send billions of dollars of weapons to Ukraine, and threaten Russia with its nuclear arsenal (which is also what backs up NATO)?