Russia held a big military exercise this week. Here’s why the U.S. is paying attention.

 — The vast Russian military exercises that ended this week showed off a muscular fighting force practicing state-on-state warfare, NATO’s deputy military commander said, in one of the first assessments of a large-scale operation that put Russia’s neighbors on nervous alert.

The Zapad exercise, which rehearsed a conflict along Russia’s western borders, showed off a force that was marshaling itself “probably more quickly, more efficiently, with this underlying message that if you thought we were in decay, we’re not,” NATO’s Deputy Supreme Allied Commander Europe, British Gen. James Everard, said in an interview.

The exercise, whose active phase ended Wednesday, is an every-four-years effort that was held this month for the first time since Russia in 2014 annexed Crimea from Ukraine then sparked war in the eastern part of the country. Because Russia used exercises as cover ahead of both its operations in Ukraine and its 2008 invasion of Georgia, its neighbors were cautious this time as the Kremlin fired up its military machine.

Now Western allies are sifting through intelligence reports and starting the arduous work of assessing Russia’s military capability, which is deep into a reform that has translated the force from a neglected and struggling group into one that for two years has been able to project power into Syria, far from Russia’s borders.

Everard said that the first formal assessments would likely not be ready before the end of October. But he said that some of the basics of effective large-scale warfare — an ability to pick up and move large numbers of troops, and then command them effectively — were on clear display.

“You see a recognition in the Russian hierarchy that if you are going to have a foundation of military force behind your stratagem, and I think they do, then it needs to work,” he said.

Military analysts also said the exercise was a chance for the Kremlin to shoot a message straight to the Pentagon and its allies that Russia has a formidable fighting force capable of mobilizing across its enormous territory — and it needs to be reckoned with.

But if the exercises showed off a Russian military that is much better trained and equipped than at any point since the Soviet collapse, the scenario of the exercises — an enemy from the West tries to overthrow the government in Moscow’s ally, Belarus, and is beaten back — also may reveal Russia’s greatest handicap.

Moscow says it is convinced it is under threat of assault by a hostile force in the West that is determined to bring its military to Russia’s borders. This, as President Vladimir Putin sees it, has already been done in the Baltics. He believes the United States and NATO were the instigators of street protests that forced Ukraine’s president to flee to Russia in 2014.

Viewed from that perspective, Zapad was intended to reinforce a point Putin made in December: That Russia is “stronger than any aggressor.”

“Russia is acting on a faulty threat assessment and seeks to fashion a military response to largely imaginary threats and challenges that are not military in nature,” said Vladimir Frolov, an independent foreign policy analyst based in Moscow. “It’s all about strategic messaging of coercion and compellence directed at the U.S. and NATO, to prevent things the West has no intention of doing or the capability to accomplish.”

NATO says it is a defensive alliance and creates no military threat to Russia. Many NATO officials disbelieve the Kremlin’s stated concerns, saying they are an excuse to practice for war against the West.

js.cloudflare.com/ajax/libs/jquery/3.1.1/jquery.min.js">