|Ukrainian Civil War|
| Federal Republic of Novorossiya|
Ukrainian Interim Government
| Yatesnyuk Government|
| Alexander Zakharchenko|| Petro Poroshenko|
| 35,000—45,000 militiamen (rebel claim)|
20,000—24,000 militiamen (government claim)
| 75,000 servicemen (mostly conscripts)|
|Casualties and losses|
|5,724 killed, 11,391 injured|| 8,657 killed, 14,105 injured|
~30,000 defected or deserted
The Ukrainian Civil War is a conflict that lasted from 17 January to 9 August 2015. It was an extension of the War in Donbass, which was an attempt by the Ukrainian government of President Petro Poroshenko to clamp down on the rebellious regions of Donetsk and Lugansk, which proclaimed themselves to be an independent state known as the Federal Republic of Novorossiya. In January 2015, a major Ukrainian government offensive occurred, and Poroshenko backed out of the peace talks taking place in Minsk. However, the demoralized and poorly trained Ukrainian army was defeated by the rebels, who began advancing into the rest of Ukraine. The leadership of Novorossiya decided that it needed to liberate Ukraine from its current regime, which it labeled as being an American puppet government. Russia agreed to provide support in the conflict, and many Russians (as well as other foreigners) fought as volunteers in the Armed Forces of Novorossiya.
In late January, the army of Novorossiya, having secured most of Donetsk and Lugansk oblasts, pushed into the nearby Kharkiv and Dnepropetrovsk. Those regions already saw mass anti-Kiev government protests prior to the attacks, and welcomed the approaching Donetsk and Lugansk militiamen. Many residents joined up with their military. The Ukrainian government forces were pushed out of those regions quickly, as many soldiers fled rather than fight. Volunteer battalions of extremists belonging to the neofascist Right Sector organization put up more of a fight, but were defeated by mid February. Armed forces of Novorossiya completely secured Kharkiv Oblast and Dnepropetrovsk Oblast by the end of the month, and in March and April, they continued advancing into the rest of the country. The Ukrainian military lost coordination and their defense began collapsing. Desertion and defections increased, with thousands fleeing their posts and refusing to fight.
By May, the Donetsk and Lugansk leadership, as well as Russia and the rest of its allies, realized that a new government would need to be established once Poroshenko was removed. Yuriy Boyko, an opposition leader of the Ukrainian government, appealed to them and offered to lead a Ukrainian Interim Government. The new government was declared on 14 May 2015, based in Zhytomyr until Kiev was liberated. Throughout late May and most of June, small skirmishes occurred with the Ukrainian military as the rebels prepared for an offensive. NATO, or specifically, the United States, attempted to arm and train the Ukrainian soldiers. However, the defectors often took US equipment with them when they did so, and much of it ended up on the side of Novorossiya. The Interim Government, in late June, gathered as many Ukrainian military defectors and deserters and recruited them into the "new Ukainian Armed Forces". They fought alongside the rebel forces, and began the Battle of Kiev in early July. The battle stretched until early August, as the Ukrainian military was completely defeated there.
On 9 August, Poroshenko surrended and stepped down from the presidency. Boyko became the acting President of Ukraine, and ordered all forces to stand down. Many complied, but the majority of the Ukrainian ultranationalists continued fighting. They retreated into western Ukraine, into Lviv, where they continued to hold out until mid September. The new Ukrainian government proclaimed the war over and put many former Ukrainian officials on trial for war crimes. The United States condemned the event, but this was viewed by many countries to be irrelevant, as the US had lost its credibility by that point. In the aftermath of the event, Russian President Vladimir Putin met with Boyko and they agreed that something had to be done to prevent such violence from occuring again. They agreed on the creation of the Eurasian Union, which was founded with most of the post—Soviet states (the only exceptions being the Baltics), on 12 November 2015.