Because, hysterical capitals notwithstanding, the USA created the mess
The US probably did contribute to to the mess, if we go back to our (and the Saudis, the Turks and the Europeans) intentional destabilization of Syria during the so-called "Arab Spring". The US continued that disfunctional policy until 2017, when President Trump halted it. (It's the same policy that the US and Europeans used to turn Libya into a failed state, that reduced Yemen to failed state status and almost handed Egypt over to the Muslim Brotherhood.) Most of the Europeans were belatedly out by 2018. Today the hugely Islamist forces in Idlib are largely supported by Turkey and Qatar. What all that bullshit accomplished was spreading civil war throughout Syria, destroying the country without removing Assad from power, and without much thought for what would replace him. And yes, that was the anarchic vacuum in which ISIS festered.
Of course the proximate "mess" was created by Turkey deciding to send its military across the border against the Kurds.
and were never, despite repetition of the same misconception, in any danger of having to go to war against Turkey.
How do you propose Turkish tanks be prevented from crossing the Syrian border?
All they had to do was refuse Turkey permission to commit genocide
I think that you dramatically overestimate the power that the US has around the world.
The United States is in no position to "refuse Turkey permission". If we shouted "We forbid you!!" at Turkey, they would have simply sneered and rolled their tanks anyway. That's because it's in Turkey's interest to suppress
the PKK, which is agitating for Kurdish independence in eastern Turkey and has been complicit in a number of terrorist acts. Turkey has its own motives, which have little to do with the United States.
Of course if we are talking non-military leverage that might get Turkey's attention, trade sanctions might work. And collectively the European Union has far larger trade with Turkey than the United States does. (They border on Turkey. At least on paper, Turkey is still a candidate to join the EU.)
Just look at Germany alone. 9.6% of Turkish exports go to Germany, and only 5.5% to the US. 9.1% of Turkey's imports come from Germany, and only 5.1% from the US. Germany's a smaller country and it conducts 80% more trade with Turkey than we do. And that's just one EU member. If the entire EU announced a 100% total halt to trade with Turkey unless Turkey withdraws, Turkey might pay attention.
Will the EU do it? Of course not. It's so much easier to blame everything on the United States.
and make further military aid contingent on compliance with previous treaties.
What treaties? The Turks have entered what is
de-jure Syrian territory. As such, any applicable treaties would be those with the Syrian government. The Turks have as much legal right to be there against the wishes of Damascus as the United States does (in other words, none).
Regarding military cooperation, we have already cut Ankara out of the F-35 program. That was our biggest arms program with Turkey.
If Canada, or the EU, were to mount a military offensive against Turkey, it would effectively
1. unilaterally dissolve NATO
I think that Turkey's current membership in NATO already has a big asterisk next to it.
2. incur the wrath of the US - or whichever components of that fragmented administration is currently in charge.
Are you sure the US would object? We probably would be concerned about the war's destabilizing effects. (Effects that would even be bigger if we were fighting it.) We would probably be doubtful whether Canada has the military strength to fight Turkey.
That's not a step any sane government would take lightly, and that no government could possibly take during an election.
Exactly.
