Comment by simon1ltd

Ukraine was guaranteed protection of its then current borders by the US, Russia, and the EU nations if it agreed to give up it's nuclear weapons.

A quick google gave me this as a top result: https://www.npr.org/2022/02/21/1082124528/ukraine-russia-put...

We should have given them this support when Russia took crimea, but didn't. The least we can do now is follow through on our agreement.

(Plus all of the other reasons in this thread -- there are fantastic reasons for the western nations to support Ukraine's defense separate from those I'm referring to here)