NATO countries commence military drill, in eastern Europe, on a massive scale not seen since the Cold War.
In a show of strength, NATO kicked off a military drill in Poland on Monday, the largest of its kind since the Cold War, amid growing tensions with Russia.
The war game, dubbed Anaconda-2016, is a military exercise involving 30,000 troops from 24 countries. America contributed 14,000 troops. The exercise also includes 12,000 Polish troops, 800 British and more from non-NATO countries.
The move will likely further damage already strained relations between the Kremlin and the West.
US Army Chief of Staff, Mark Milley, said American participation "demonstrates that we are shoulder to shoulder with the Polish people" and that the exercises would "improve our collective readiness."
NATO says exercises such as Anaconda-16 and plans for an increased military presence in the region are a defensive reaction to Russia's 2014 annexation of Crimea from Ukraine.
Russia is adamantly opposed to the move, which NATO refers to as its "deter and dialogue" strategy.
Russia has warned of retaliation after accusing NATO of threatening its security by expanding eastwards. Defence experts warn that any mistake by NATO forces could instigate a military response from Moscow.
NATO officials have expressed their own concerns about Russia's military exercises in which thousands of Russian troops conduct war games without giving the alliance any prior warning. In addition, Russian jets routinely breach Nordic countries' airspace.
The war game, which includes drills such as a night-time helicopter assault and the dropping of US paratroopers to build a temporary bridge over the Vistula River, precedes a NATO summit in Warsaw that will approve more troops to be stationed in Eastern Europe.
The military operation comes on the heels of the US activating a ballistic missile shield in Romania, as part of a "defence umbrella" that Washington says will span from Greenland to the Azores.
Last month, construction began on a similar missile interception base in northern Poland.
The war game serves as a test for the level of cooperation between NATO countries in mobilizing against military and chemical threats. It represents the biggest mobilisation of foreign allied troops in Poland during peacetime.