Under the current circumstances we cannot say "no".

She's adjusting more and more to the new circumstances.

You can say that the circumstances were thus in the period leading up to the declaration of war.

Under no circumstances should you go away today.

I wouldn't go under any circumstances.

The massacre in Norway and the recent rebellion and the booty in England, are dreadful in consideration of the circumstances that the world drifted into.

It will not be long before you accommodate yourself to the new circumstances.

Who's more likely to remember the circumstances of when this photo was taken?

Under normal circumstances, I'd agree to do that.

A conspiracy theory is thinking that blames or explains an important event or set of circumstances on a secret plot that is usually masterminded by powerful people. Conspiracy thinking can also embrace the idea that a big secret is being kept from the public.