The US attempts to change regimes in Ukraine, Iraq, Afghanistan, Syria and Libya have not worked. The US simply does not know how to do it.
It was not the United States, but Russia that triggered the military conflict in Ukraine.
The spontaneous onset of massive Euromaidan protests was a reaction of the Ukrainian population to the sudden departure of President Yanukovych from the Association Agreement with the European Union and to the brutal dispersal of student protest actions on 30 November 2013. A similar case is available here.
The EU condemns the clear violation of Ukrainian sovereignty and territorial integrity by acts of aggression by the Russian armed forces since February 2014.
The Office of the Prosecutor of the International Criminal Court recognised that “the information available suggests that the situation within the territory of Crimea and Sevastopol amounts to an international armed conflict between Ukraine and the Russian Federation". The international armed conflict began at the latest on 26 February 2014 when the Russian Federation deployed members of its armed forces to gain control over parts of the Ukrainian territory without the consent of the Ukrainian Government.
The European Union stated in July 2014 that "arms and fighters continue flowing into Ukraine from the Russian Federation". At the NATO Summit in Wales in September 2014, NATO leaders condemned in the strongest terms Russia’s military intervention in Ukraine and demanded Russia to stop and withdraw its forces from Ukraine and from the country’s border. NATO leaders also demanded Russia to comply with international law and its international obligations and responsibilities; refrain from aggressive actions against Ukraine; halt the flow of weapons, equipment, people and money across the border to the separatists; and stop fomenting tension along and across the Ukrainian border.
In 2015, Russian President Vladimir Putin admitted Russia's military presence in Ukraine.