This week, SU-24 fighter-bombers buzzed a U.S. destroyer in the Baltic Sea. The Russian planes carried no missiles or bombs.

Message: What are you Americans doing here?

In the South China Sea, U.S. planes overfly, and U.S. warships sail inside, the territorial limits of islets claimed by Beijing.

In South Korea, U.S. forces conduct annual military exercises as warnings to a North Korea that is testing nuclear warheads and long-range missiles that can reach the United States.

U.S. warships based in Bahrain confront Iranian subs and missile boats in the Gulf. In January, a U.S. Navy skiff ran aground on an Iranian island. Iran let the 10 U.S. sailors go within 24 hours.

But bellicose demands for U.S. retaliation had already begun.

Yet, in each of these regions, it is not U.S. vital interests that are threatened, but the interests of allies who will not man up to their own defense duties, preferring to lay them off on Uncle Sam.

And America is beginning to buckle under the weight of its global obligations.

And as we have no claim to rocks or reefs in the South China Sea — Vietnam, Taiwan, Malaysia, Brunei and the Philippines do — why is this our quarrel?

If these rocks and reefs are so vital they are worth risking a military clash with China, why not, instead, impose tariffs on Chinese goods? Let U.S. companies and consumers pay the price of battling Beijing, rather than U.S. soldiers, sailors, and airmen.

Let South Korea and Japan build up their forces to deal with the North, and put Beijing on notice: If China will not halt Kim Jong Un's nuclear weapons program, South Korea, and Japan will build their own nuclear deterrents. Half a century ago, Britain and France did.

Why must we forever deter and, if need be, fight North Korea?

And why is the defense of the Baltic republics and East Europe our responsibility, 5,000 miles away, not Germany's, whose economy is far larger than that of Russia?

Even during the darkest days of the Cold War, U.S. presidents refused to take military action in Hungary, Czechoslovakia or Poland.

When Moscow intervened there, the U.S. did nothing. When did the independence of Eastern Europe become so vital an interest that we would now risk war with a nuclear-armed Russia to ensure it?

Under Article 5 of NATO, an attack upon any of 28 allied nations is to be regarded as an attack upon all.