Jesus could have given up on different moments during his earthly lifetime, but he didn't! Many others could have resigned to the opression imposed to them by much larger and more powerful empires (Exodus from Egypt, Gideon and the Small Army, David versus Goliath...), but they didn't, because they were loyal to those divine principles, and consequently loyal to God.
Christians don't want war, but they have to defend themselves if war is declared to them. It's Ukraine's right to defend their territory, their home, as you would do if someone attempted to invade your house.
You hit the nail right on the head. Ukraine attempted to defend their territory, but they failed. They failed to win against the US/CIA takeover of the Ukrainian government in 2014. And they failed to dislodge the United States and Nato from their government ever since. So, they die uselessly. Do you think Zelensky is Christian? You have missed a lot if you do.
I'm sure Russia had different motives for going into Ukraine in 2022. But among them was the desire to protect Russian and Ukrainian people in the whole area that Russia has taken over since. Protect them from what? Protect them from being killed by the Ukrainian government. It's a shame that the US was/is simply using Ukraine to try to conquer Russia.
Why was the Ukrainian government killing its own in the Donetsk areas since 2014? Because these people were in favor of Russia more than they were in favor of the US. It's like you said. The country has the right of self-defense. But since the US controlled the government, people in favor of Russia were persecuted.
So you see, it isn't as simple and straightforward as you seem to think. And the result of the funding and armament the US sent to Ukraine is the deaths of possibly more than 400,000 soldiers, the vast majority Ukrainians. But it seems that the US wants to kill the rest of the Ukrainian people off, too. They are still pushing armament and funds in.
And while we will never know for sure, because it can never be done over the other way, probably Russia would never have entered Ukraine if people were not being killed by the Ukrainian government. Russia would have been happy to simply buy from Ukraine whatever else it needed, including passageway to the Black Sea.
EDIT: A little about the "Orange Revolution" in Ukraine: