Of our 13 ground combat divisions (active duty), there are of course scenarios where most would deploy. The worst would be a Soviet invasion of say Lithuania or Estonia or Latvia, or perhaps Poland. I don't view that as likely, the Russkis are not in good shape.
Another would be the Korean peninsula, I don't view that as likely either. Another would be Taiwan, though we'd probably try and maintain distance there, not ground forces.
One reason these things are not likely is those 13 divisions.
We went into Iraq with 2 divisions reinforced as I recall, 4th ID was held up in Turkey. That was plenty to destroy the Iraqi military and not nearly enough to stabilize the country. If you break it, you own it.
I lean to think we could go to a larger reserve force and smaller active, but I'm not sure about that of course. The IRR is there as well, and then the NG, which is not in great shape according to one member of my family.