You misunderstand UN approval and assistance.
The UN has no bearing on whether the US intervenes in an area.
There is no taking away of sovereignty if the UN agree on an action...none.
We went to both Afghanistan and Iraq due to US presidential action and congressional approval.
There’s no doubt we did, but the UN ended up getting dragged in too because of
the kind of post World War 2 international law kind of world we live in.
Rumsfeld said these wars in Iraq and Afghanistan weren’t like World War 2 and he’s right. They are limited wars not wars seeking a total and complete victory over the enemy like Roosevelt got over Germany and Japan.
Pakistan meddles in Afghanistan and Iran meddles in Iraq.
Both those nations should have been dealt with to obtain total victory in the wars but were not. One (Pakistan) has nukes and the other (Iran) is developing them. Those were probably the clinchers to deter action just like the fear of killing Soviets (nuclear country) preventing the bombing of Haiphong harbor that would have won the Vietnam War.
W Bush and Obama failed to take these wars to total victory and we are left holding the bags we hold now. No victory in Afghanistan with Pakistani meddling and an Iraq left dominated by Iran.