[Alvin Walton]

Russian expansion and aggression - I doubt sanctions would do anything.
They're to big.
Assassinating Putin and his immediate lieutenants would be nice if it couldnt get traced back to the USA.
It would send Russia into a tailspin.

China - Very tough call. We are deeply in bed with them (trading)
The South China Sea islands - They are claimed by at least 6 nations.
The Philippines are one.
I'd explore helping them put an airfield on one of the islands with the notion of allowing our aircaft to "visit" there.

Iran - I would rescind all deals.
Then change the rules of engagement in the Straits of Hormuz.
Their navy would do something very stupid soon after that.
And then right after that their navy would cease to exist.
I would then sanction them every way possible and then and try to force a revolution to get them out from under the ayatollahs.

North Korea - since they threaten us all the time I would just wait till they do it one more time.
Then I would force a build up and a blockade over there and make them flinch.
Then I'd drop a feckload of cruise missiles on their nuclear facility's and all of fat fuck Kims hideouts.

And yes, it is easy for me to say this from my recliner.