This is what is correlated with US dollar strength

Here's the graph:

source

Is dollar strength a cause or an effect? I think it's an effect. For example dollar strength didn't cause the eurozone crisis - it was the opposite way round. The eurozone crisis caused holders of the euro around the world to panic, sell euros and buy dollars.

The dollar acts like the canary in the coal mine. It's a sign something bad is happening in the world, and billions of money are on the move.