A short summary can be a good start to answer the question. In August 1991, President George H. W. Bush delivered a speech to the Kiev Parliament in which he urged Ukrainians to seek autonomy rather than independence. He feared that the disintegration of the USSR would destabilise the entire region. He went unheard; and a new phase began, in which Ukraine started fluctuating, depending on its leaders, between the West and the East. In Washington, meanwhile, the line of those who wanted to take advantage of Russia’s decline to extend NATO to all the countries of the old Soviet zone of influence prevailed.
While Bush Senior would have rather kept Ukraine in the Russian orbit, his son, George W. Bush, who was elected president in 2001, proposed in 2008 that Ukraine and Georgia become NATO members. When a nightly vote in the Kiev parliament removed from office the pro-Russian president and the new Ukrainian leadership opted for an association agreement with the European Union rather than accepting Putin’s offer to a number of former Soviet Union republics, Russia’s reaction was immediate. Its leader came to the conclusion that the agreement with the EU, as it already happened with the old satellites of the USSR, would precede entry into NATO and manifested his opposition by taking over a region that had only been Ukrainian since 1954 (Crimea), and where the majority of the population was Russian.
Was it a mistake? Other reactions would have been possible and desirable. But, from that moment, it was clear that Russia would consider Ukraine a potentially hostile country and that it would not tolerate, without reacting, further progress of the Atlantic Alliance on its western borders. Since then, there has been a sort of parallelism between the American policy towards Russia and that of Russia towards Ukraine. The United States, after the annexation of Ukraine, imposed economic sanctions on Russia in the hope of arousing the discontent of civil society against Putin’s regime; while Russia, for its part, is doing the same by getting in the way of Ukrainian ships crossing the Kerch Strait to reach the two Ukrainian ports on the western coast of the Azov Sea. After the loss of Sevastopol, Mariupol and Berdyansk have become the maritime gates of a country that has long been a precious barn for the countries bordering the Black Sea and the Mediterranean.
The 25 November incident was probably a provocation. Ukrainian President Petro Poroshenko is on the eve of the election to renew his mandate, and the polls are not favourable for him. He probably hoped that an international crisis would guarantee him the support of his western friends and would make him indispensable even for those voters who, in other circumstances, would not have voted for him. The other two leaders involved are not in better shape. Putin is much less popular in his country since he decided to extend his working life and delay his retirement. It is not excluded that the patriotic card, played thanks to the crisis, will give him back at least part of his lost popularity. Trump seemed determined to improve relations with Moscow, but since the Russian services have been suspected of sabotaging Hillary Clinton’s electoral campaign to promote his election, the American president must guard his back against the risk of impeachment. NATO’s reactions were predictable. The old USSR satellites, now members of NATO, consider Putin’s Russia an enemy, while a large share of the American political class has decided to treat it as a dangerous reincarnation of the Soviet State.
A solution to the crisis exists: a neutral Ukraine in the spirit suggested by Bush Senior. However, the number of those who believe that they will benefit from a crisis has grown considerably, and we have come dangerously close to the point where each of the two contenders believes that it is up to the other to take a step back. Paradoxically, these crises could be more severe than those that erupted during the Cold War. There was then a conviction in each of the two camps that the opponent would make use of its nuclear arsenal. We cannot be sure that today’s players will be as cautious.