U.S. troops rode to the rescue again in this month in Poland. Photographer: Sean Gallup/Getty Images
U.S. troops rode to the rescue again in this month in Poland. Photographer: Sean Gallup/Getty Images

When the Baltic states and Poland recently wanted to show Russia that their countries are under the full protection of the North Atlantic Treaty Organization, the U.S. sent them about 600 troops for exercises.

The gesture was small, but telling: American boots were needed to convince Russia -- not to mention Latvians and Poles -- of NATO's commitment. Europe has so hollowed out its collective military, and is so divided over how to answer open aggression, it struggles to offer a credible deterrent of its own.

No matter how the crisis in Ukraine unfolds, Europeans need to rethink their defenses. They can no longer afford to rely so heavily on the U.S. Nor can they go on regarding Russia as a benign long-term partner with whom they can soon return to business as usual.

Europe's nonchalance about defense has been a problem for a while, but until recently it didn't seem to matter. When the Cold War ended, European countries cut their defense budgets as the U.S. drew down its forces on the continent, sure in the delusion that European wars were a thing of the past. So sure, indeed, that France contracted to sell Russia two sophisticated Mistral class helicopter carriers, even after Russia's 2008 invasion of Georgia.

The chart below shows how, over the past five years, defense spending has rocketed in emerging powers such as China and Russia, while it has declined in Europe. Germany now spends just 1.4 percent of gross domestic product on defense. The EU average is 1.6 percent, compared with 3.8 percent in the U.S. and 4.1 percent in Russia.

Europe has plenty of troops to fend off Russia's conventional forces, which though improving are much diminished since the collapse of the Soviet Union. Yet this isn't just about personnel, it's about combat-readiness. In 2011, the U.S. and the European Union had roughly the same number of men and women under arms, but the U.S. spent about four times as much equipping them to fight -- about 102,000 euros ($142,000) per soldier, compared with 24,000 euros in the EU.

Viewing Europe’s forces collectively in this way amounts to a triumph of hope over experience. The countries duplicate resources and have rarely come together around a unified purpose. Although, for example, the EU has had joint battle groups operational since 2007, a lack of political agreement on missions has kept them from ever being deployed.

It isn't as if Europe needs to engage in an arms race with Russia, but its long slide in defense spending must end. Financially troubled governments, facing no direct threat from Russia, will be tempted to do little. Yet Russia has proved itself unpredictable and expansionist at a time when the U.S. is increasingly stretched to meet defense commitments in Asia. Today's U.S. decision to sanction seven more individuals who are said to be close to President Vladimir Putin may or may not succeed in moderating Russian behavior in Ukraine, but in the longer term Europe must boost its defenses.

Sweden (not a member of NATO) showed the way last week, when it pledged to boost defense spending by $833 million a year and buy additional aircraft and submarines to protect its interests in the Baltic Sea. After finding itself with no jets to intercept a Russian incursion last year, Sweden has made it a priority to be able to respond to threats quickly. These are the kinds of concrete commitments that NATO members should prepare ahead of their next summit, in September.

Years of talk on "pooling and sharing" troops and hardware should also finally turn into action -- starting with France selling those helicopter ships to NATO, rather than Russia. There is precedent for the alliance collectively owning and operating expensive equipment, in the AWACS surveillance aircraft that are now watching Ukraine from Polish and Romanian airspace.

Russia sees the struggle over Ukraine as a turning point as significant as the fall of the Berlin Wall in 1989. Putin has made it clear that in the 21st century, Europe's borders can be changed by force. The next time he considers an invasion, as in Ukraine today, he will stand down only if he calculates that the military and economic costs are too high: Europe must be capable of making them so, with or without U.S. help.

To contact the senior editor responsible for Bloomberg View's editorials: David Shipley at davidshipley@bloomberg.net.