Fighting started in April 2014 and raged for months until Ukraine and the separatists came to a deal on 5 September to halt the violence and free prisoners.
But the ceasefire never held entirely. Although the intensity of the conflict subsided, the clashes never really ended and both sides used the relative lull to build up their forces.
Battle raged for control of the ruined airport at Donetsk, with Russian-backed rebels trying to seize a strategic and symbolic asset.
A new rebel push began with the start of the year, culminating in the capture of the airport's main terminal on 22 January.
Violence has flared the length of the September ceasefire line and the casualties mounted:
- Civilians were killed by shells and rockets in rebel-held areas, particularly the cities of Donetsk and Luhansk
- Thirty people died in the Ukrainian port city of Mariupol, in an artillery attack that international observers said came from rebel-held areas
- Rebels launched a concerted attack to seize the town of Debaltseve, a transport hub held by government forces
Each side accused the other of tearing up the peace deal.
For the government, it was the rebels' decision to hold their own local elections in November 2014, in defiance of the Kiev authorities.
The separatists, however, were unhappy that the government had responded by saying it would scrap the special status of their two regions, Donetsk and Luhansk.
Among the terms of the truce were a commitment to pull back heavy guns from the front line by at least 15km (9 miles), a release of prisoners and an agreement for international observers to monitor the truce and a buffer zone on the Ukrainian border with Russia.
Ukraine would also grant wider self rule to Donetsk and Luhansk.
Long story short...things are heating back up.