Russia is modernizing its military and threatening its neighbors. Is a confrontation coming? Here's everything you need to know:

What is Russia up to?

Since annexing the Ukrainian peninsula of Crimea, Russia has been throwing its weight around in Eastern Europe. Russian military planes and ships have been aggressively buzzing U.S. and NATO aircraft and vessels and intruding into European waters and airspace. Russian warplanes recently flew simulated attack passes at an American destroyer in the Baltic Sea, and in April, a Russian warplane did a dangerous barrel roll over an American fighter jet, passing within just 25 feet. In May, British fighter jets intercepted three Russian military transport aircraft — which could carry troops or heavy equipment — approaching NATO member Estonia and refusing to answer hails. British Defense Secretary Michael Fallon described the incident as an "act of Russian aggression." These provocative actions have occurred at the same time as Russian President Vladimir Putin has been modernizing and upgrading his military forces.

Why the upgrade?

Putin inherited a lumbering and antiquated military from the Soviet Union, along with status as a second-rate power. He wants Russia to once again become a credible counterweight to the U.S. and NATO, and protect its dominion over its traditional sphere of influence. To that end, he has spent billions on a new generation of nuclear missiles as well as new tanks and fighter jets. The Russian military plans to vastly increase its manpower too, announcing 40 new brigades by 2020, on top of the 70 brigades it already has. Whether it can deliver on that plan, though, is debatable, since the oil price slump has hit Russia hard, depriving Putin of needed revenue. But Russia has nonetheless been moving troops and weapons closer to the borders of its neighbors and NATO members. Its Black Sea Fleet, headquartered in the Crimean port of Sebastopol, recently added a dozen warships and has been sending them out on patrols near the Bulgarian, Romanian, and Turkish coasts. "The Black Sea has almost become a Russian lake," said Turkish President Recep Tayyip Erdogan.

Could Russia rival the U.S.?

There's no chance of that. Even the top Pentagon brass — who are using Putin's buildup to argue for greater funding — don't believe American military supremacy is in jeopardy. The U.S. still spends nearly seven times more on defense (about $600 billion) than Russia ($84 billion), and has 19 aircraft carriers to Russia's one. And NATO has four times Russia's military power. Under treaties signed by recent presidents, including George W. Bush and Barack Obama, the two sides have approximate nuclear parity, but the U.S. has hundreds of nondeployed warheads in storage, and Russia does not. Because of these imbalances, says military analyst Daniel Gouré, Russia is relying on intimidation and unpredictable behavior, in the hope that NATO will "accept a small defeat rather than risk a big war" — the very tactic it has used in Crimea and Ukraine. To ratchet up Western fear, Russia has even suggested it would use nuclear weapons in local conflicts.

What is NATO doing in response?

Worried that NATO is unprepared for a sudden Russian offensive, the Obama administration is moving 5,000 troops, and tanks and other heavy weapons, into several Baltic and Eastern European countries. NATO is also getting around to deploying missile defense systems in Poland and Romania that were originally proposed in 2002, when the U.S. was still reeling from 9/11 and worried about Iran getting the bomb. A base in Romania became operational just a few weeks ago, and work has begun on another in Poland. Moscow is livid, and argues that since Iran has now been prevented from obtaining a nuclear weapon, the missile defense system must be aimed at Russia, in violation of several treaties. NATO officials counter that Russia has almost certainly already violated those treaties by placing nuclear weapons in Kaliningrad, a tiny exclave of Russian territory nestled between Lithuania and Poland on the Baltic Sea.

Is that the next flash point?

It could be. Last December, Russia conducted a snap military drill in Kaliningrad, bringing its forces to the highest state of alert just miles from two NATO capitals. Some analysts believe it could begin manufacturing crises around access to Kaliningrad as a form of blackmail, to pressure NATO to roll back its missile defense program or even formally recognize the annexation of Crimea.

What will happen next?

NATO plans large-scale war games involving 10,000 troops in Poland in June, just ahead of a major NATO summit meeting in Warsaw. There, President Obama will meet with heads of all NATO member states, and Russian aggression is expected to be a major topic. NATO says it wants to keep talking with Russia, and it has reconvened a NATO-Russia council that stopped meeting after the Crimea annexation. But NATO no longer speaks of a "strategic partnership" with Russia, but rather uses Cold War–era rhetoric about keeping lines of communication open. Russian officials, meanwhile, are taking a belligerent and pessimistic tone. The world "has slid into a new Cold War," said Russian Prime Minister Dmitry Medvedev.

Moscow's ongoing cyberwar

Russia now outstrips China as America's biggest cyberthreat. "Russian cyber actors are developing means to remotely access industrial control systems used to manage critical infrastructures," National Intelligence Director James Clapper said. Hackers with ties to the Kremlin have already penetrated computer systems at the Polish stock exchange, a French TV station, The New York Times, NATO, and even the White House and the Pentagon. Much of the hacking is for harassment and espionage, but at times it also presents a physical threat. In 2014, Russian hackers took over a computer that controlled the blast furnace at a German steel mill, inserting malware that caused the machine to melt down. Russian cyberattacks on Ukraine have taken out part of the power grid and interrupted military communications. In Syria, Russian jamming systems interfere with NATO spy satellites. "Russia certainly has been more active than any other country in terms of combining cyberattacks, or cyberoperations, with [military] operations," said security expert Jeffrey Carr. "China has never done anything like that."