Then-Ukrainian President Viktor Yanukovych pledged to sign the deal - but walked out on it at the last moment. Mass protests followed in Kiev, decrying Yanukovych for what was seen as an attempt to deny Ukrainians a European future. A crackdown by riot police saw 130 people killed in sniper fire. Yanukovych fled to Russia.
Annexation and violence
Russia annexed the Crimea in 2014 after troops without insignia occupied crucial infrastructure, including Ukrainian military bases, while Ukrainian troops put up little resistance and retreated. It was only years later that Russian President Vladimir Putin publicly admitted that these were in fact Russian troops.
Activists in eastern Ukraine, backed by Russian operatives, took over towns and tore down Ukrainian flags. Separatist leaders in the cities of Donetsk and Luhansk held elections supporting a motion to break away from Ukraine.
Sporadic violence grew into a full-blown conflict in May 2014, when Ukraine launched an airstrike on the Donetsk airport that was overrun by Russian Chechen fighters. More than 10,000 people have been killed and over one million displaced, with large parts of the east still under separatist control. The Kremlin never admitted its role, portraying it as a civil conflict, but overwhelming evidence suggests Russia has been sending a sizeable number of troops and advisers as well as weapons to the rebels.
Ukraine signed peace accords with the separatists in 2015, calling for a ceasefire and political settlement in the east. While it helped to decrease the intensity of fighting, the accords did nothing to resolve the region's political stalemate.
Escalation at sea
The latest area of rising tension occurred on Monday in the Kerch Strait, which links the Sea of Azov and the Black Sea off the eastern edge of the Crimean Peninsula. Russia has built a long bridge spanning the strait and connecting the peninsula with its mainland. In March, Ukraine detained a fishing vessel sailing from Crimea, and Russia increased its military presence in the area, inspecting all vessels sailing to or from Ukrainian ports, disrupting trade. Ukraine has protested, calling them an "economic blockade" affecting its ports in the industrial east.
Ukraine says two of its naval gunboats and a tugboat were fired on and seized by the Russian coast guard in the narrow strait. Russia says the Ukrainian vessels violated its territorial waters. Both sides blamed the other in the incident. The ship seizure has raised questions about eventual international intervention. Nato and the UN Security Council discussed what to do. The EU is calling on both sides to stay calm.
Church conflict
In another sign of Ukraine's resolve to break with Russia, Kiev has stepped up efforts to seek independence for its Orthodox church. The church in Ukraine has been tied to the Moscow Patriarchate for hundreds of years, but calls for independence have increased since the conflict began.
The Istanbul-based patriarchate made the first step towards recognising the independence of the Ukrainian Orthodox Church in October. The move was decried by the Russian Orthodox Church.
What's next?
While Monday's incident raises the spectre of a full-blown conflict between Ukraine and Russia, it is not likely that either wants an all-out-confrontation, and the leaders of both countries might be getting an outcome that they want.
Putin, whose approval ratings have tumbled recently, reinforced the message that Crimea is Russian for good and that he won't allow anyone to question it.
Ukrainian President Petro Poroshenko is likely to benefit from Ukraine's Parliament voting to impose martial law in the country for 30 days. Poroshenko's approval ratings have been plunging, and playing up the Russian threat could help his chances of getting re-elected on March 31.
- AP
