"Just started" in... September? Right! Yes, Obama opposed the specific foreign acts you mention, but he got international cooperation to enact serious sanctions. You'd prefer armed war with Russia, Syria, and China? How much global policing are you willing to pay for? Unlimited amounts? You do know how successful Vietnam, Afghanistan, and Iraq adventures were, I suppose? Obama left no vacuum: he didn't begin the Iraq war that inarguably wrecked that entire area. N. Korea became a problem for Trump when it wasn't such of a major one for Obama after 8 years. Why do you think NK waited for Trump to take office? 
Reagan killed the Soviet Union? You mean Communism was a going concern and it's a successful economic option? You may wish to read some historians besides Fox news commentators to get a little more depth on the collapse of that "empire." 
You forget about the bombing of the Marine barracks? Reagan did. 241 American soldiers died and Ronnie did NOTHING. Bumpus.
Obama killed OBL.