The CIA gave stinger missiles to the Taliban when the Soviets were in Afghanistan. The Russians gave military hardware to the North Vietnamese when the USA was there.

Arming your enemy's enemy is nothing new.

I think the line is when your troops shoot their troops.

Providing weapons has been a US-Soviet past time for the whole Cold War.

In this case, I think the US could have even moved in troops without being at war, early in the invasion. It just needs a pretext. By far the best response a week in, when Russia claimed chemical weapons, Nazis, etc., would have been to send in a multilateral force to investigate Russia's claims. It's face-saving for the Russians and ends the war.

Tensions are too high for that now.

The Soviet Union never hesitated to supply weapons to North Vietnam when our country was at war with them. Turnabout is fair play.

It is weird right? And yet it isn't either. Selling weapons to people so they can vanquish their enemies has been a time honored tradition. If we were less invested in which side won, I wouldn't be surprised to see companies selling to both sides, because business is business right?

There are "rules" (and by rules I mean what is interpreted as "participating" vs "supporting" in a conflict that have been established and enforced for well over a thousand years. And supplying weapons has been firmly established in the 'supporting' category not the 'participating' category.

This conflict is illustrating a lot of things that haven't been seen since the cold war, which is an opportunity to learn new things about how the world works if you haven't seen it before.

The next interesting step happens when this conflict settles out, what does it look like.