In March and April 2021, Russia started to mass thousands of soldiers and military equipment near its border with Ukraine, representing the highest force mobilization since the countrys annexation of Crimea in 2014. This precipitated an international crisis and generated concerns over a potential invasion. Satellite imagery showed movements of armor, missiles, and other heavy weaponry. The troops were partially removed by June. The crisis was renewed in October and November 2021, when over 100,000 Russian troops were again massed near the border by December.The ongoing crisis stems from the protracted Russo-Ukrainian War that began in early 2014. In December 2021, Russia advanced two draft treaties that contained requests of what it referred to as security guarantees including a legally binding promise that Ukraine would not join the North Atlantic Treaty Organization (NATO) as well as a reduction in NATO troops and military hardware stationed in Eastern Europe and threatened unspecified military response if those demands were not met in full. The United States and other NATO members have rejected these requests, and warned Russia of swift and severe economic sanctions should it further invade Ukraine. Bilateral U.S.-Russia diplomatic talks were held in January 2022, but those failed to defuse the crisis.The crisis has been described by some commentators as one of the most intense since the Cold War.