This is perhaps the most dangerous point in Europe's history since the end of the cold war. Direct confrontation between Russian and Ukrainian forces will draw in the United States, one way or another. While there is still time, it's extremely important to understand what each party involved is aiming for.

Over the last 10 days, Moscow has been unpleasantly surprised several times. First, when Ukraine's then president, Viktor Yanukovych, halted an operation which would have cleared his opponents from the positions they occupied in central Kiev. Given the clear order, the Berkut riot police were closing in on the Maidan – the protest movement, named after Kiev's Independence Square, whose leaders were desperately calling for a truce, – but suddenly the Berkut advance was stopped. Instead, Yanukovych invited the opposition for negotiations. The second surprise came when the negotiations turned into talks about Yanukovych's concessions, with the participation of three European Union foreign ministers.

The agreement, signed on 21 February, was a delayed capitulation by Yanukovych – who had been seen triumphant only a couple of days earlier. An even bigger surprise was the rejection of these capitulation terms by the radicals, and the opposition supporting Yanukovych's immediate resignation. Finally, the German, Polish and French governments, who had just witnessed the Kiev accord, raised no objection to the just-signed agreement being scrapped within hours.

Russia, whose representative had been invited to witness the signing of the 21 February document, but who wisely refused to co-sign it, was incensed. What Moscow saw on 21-22 February was a coup d'état in Kiev. This development led to a fundamental reassessment of Russian policy in Ukraine, and vis-à-vis the West.

Viewing the February revolution in Kiev as a coup engineered by Ukrainian radical nationalists from the west of the country – assisted by Europe and the United States – the Kremlin believed Russia's important interests were directly affected. First, Russian president Vladimir Putin's plans of economic integration in the post-Soviet space would have to do without Ukraine. Second, the fact that radical nationalist components were among the beneficiaries of the Kiev revolution left no doubt about Ukraine's future foreign and security policy and its domestic policies.

The Association Agreement with the EU, whose signature was suspended by Yanukovych in November 2013, would now be signed, putting Ukraine, in principle, on track to long-term integration with the EU. More ominously, the new Ukrainian government would revoke the 2010 law on the country's non-aligned status and seek a Nato Membership Action Plan, or MAP. (It was the issue of MAP which materially contributed to the 2008 war between Russia and Georgia). In domestic terms, the triumph of western Ukrainian nationalists threatened discrimination against the Russian language, including in the largely Russophone eastern and southern regions, and a separation of the Ukrainian Orthodox Church from the Moscow Patriarchate. The new official Ukrainian narrative, it was feared in Moscow, would change from the post-Soviet "Ukraine is not Russia" to something like "Ukraine in opposition to Russia".

Moscow has always been thoughtless, lazy and incoherent in its strategy towards an independent Ukraine. It preferred instead to focus on specific interests: denuclearisation; the Black Sea fleet; gas transit and prices; and the like. During the early days of the present crisis, it remained largely passive. Now, things are changing at breakneck speed. With the delicate balance in the Ukrainian polity and society which had existed since the break-up of the USSR no more, Russia has begun to act, decisively, even rashly. Again, there is hardly a master strategy in sight, but some key elements are becoming evident.

Russia is now seeking to insulate the Crimean peninsula from the rest of Ukraine – to prevent clashes between Kiev's military or police forces or Ukrainian nationalist paramilitary groups, on the one hand, and the locals, on the other, as well as to neutralise the Ukrainian police and military forces permanently deployed in Crimea. Moscow has given political, economic and military support to the local, pro-Russian elements who never accepted Ukraine's ownership of Crimea, which was transferred from Moscow's to Kiev's administration in 1954. Moscow now has two options: a confederacy between Crimea and Ukraine and Crimea's full integration into the Russian Federation (a relevant law is being adjusted to allow this).

With regard to eastern and southern Ukraine, Russia will seek to support those elements who resent western Ukrainian rule in Kiev. Rather than favouring their secession, Moscow is likely to support Ukraine's decentralisation up to federalisation, which would neutralise the threat of a unified anti-Russian Ukraine within Nato. The effectiveness of Russia's efforts to mobilise opposition to Kiev in the east and south will depend on the levels of wisdom and tolerance by the new authorities in Kiev. In the worst case, a unified Ukraine may not survive.

With regard to Kiev, Moscow has balked at recognising the "coup" which many Russian state-run media and officials call "fascist" or "neo-Nazi" – a reference to the collaboration between western Ukrainian nationalists and Adolf Hitler during the second world war. Russia has not recognised the provisional government and is only maintaining "working contacts" with Ukrainian officials. To poke Kiev in the eye, Russia gave the ousted President Yanukovych personal protection on its own territory, and organised his press conference in the southern city of Rostov-on-Don on Friday. The lack of legitimate authority – the Russians say the Rada, the Ukrainian parliament, is acting under pressure from the Maidan – gives Moscow a freedom to act in "lawless" and "rudderless" Ukraine.

Unlike in 2008 in South Ossetia and Abkhazia, Moscow decided not to wait for the first shot being fired before intervening: prevention, it now evidently believes, is better than counter-attack. As in 2008, however, recognition of a breakaway region by Moscow – this time, Crimea – may become the legal basis for a Russian military presence in the area beyond the terms of the 1997 Russo-Ukrainian treaty governing the status of the Black Sea fleet. This is unlikely to be a passing moment in Russian-western relations.

In Moscow, there is a growing fatigue with the west, with the EU and the United States. Their role in Ukraine is believed to be particularly obnoxious: imposing on Ukraine a choice between the EU and Russia that it could not afford; supporting the opposition against an elected government; turning a blind eye to right-wing radical descendants of wartime Nazi collaborators; siding with the opposition to pressure the government into submission; finally, condoning an unconstitutional regime change. The Kremlin is yet again convinced of the truth of the famous maxim of Alexander III, that Russia has only two friends in the world, its army and its navy. Both now defend its interests in Crimea.

The Crimea crisis will not pass soon. Kiev is unlikely to agree to Crimea's secession, even if backed by clear popular will: this would be discounted because of the "foreign occupation" of the peninsula. The crisis is also expanding to include other players, notably the United States. So far, there has been no military confrontation between Russian and Ukrainian forces, but if they clash, this will not be a repeat of the five-day war in the South Caucasus, as in 2008. The conflict will be longer and bloodier, with security in Europe put at its highest risk in a quarter century.

Even if there is no war, the Crimea crisis is likely to alter fundamentally relations between Russia and the west and lead to changes in the global power balance, with Russia now in open competition with the United States and the European Union in the new eastern Europe. If this happens, a second round of the cold war may ensue as a punishment for leaving many issues unsolved – such as Ukraine's internal cohesion, the special position of Crimea, or the situation of Russian ethnics in the newly independent states; but, above all, leaving unresolved Russia's integration within the Euro-Atlantic community. Russia will no doubt pay a high price for its apparent decision to "defend its own" and "put things right", but others will have to pay their share, too.

Dmitri Trenin is director of the Carnegie Moscow Centre.