Is there anything us ordinary citizens can do to stop war?

It would take courage, solidarity, and the willingness to die, but ordinary citizens can start or stop just about anything if they organize and act in such a way as to win public approval in their resistance to a government. When they act like the alt left in the US has acted they hurt their cause more than help it. Well organized passive resistance can change history, but abuse and disrespect inflames matters.

Maybe if enough people made their voices heard urging calm and moderation, or maybe I'm an unrealistic optimist. I suppose the time to do it is at the ballot box.

No buddy. I wrote to my local mp asking if we could. War is money. They love money

Stop buying things from companies that give money to bad politicians.

No.