According to data from NATO, there were 4,650 troops under direct NATO command in February 2021 or a year before Russia launched its attack against Ukraine.

These troops were stationed in four multinational battle groups located respectively in Estonia, Latvia, Lithuania and Poland.

Then Russia started deploying its troops and capabilities along its shared border in Ukraine, accelerating these moves at the end of last year and in January, arguing it was a defensive move over Ukraine's NATO aspiration and the trans-Atlantic alliance's eastern expansion since the 1990s.

NATO and its 30 members reacted to the build-up of Russian troops by bolstering their eastern positions with more troops and capabilities.

A month after Russia's invasion of Ukraine started, there were 40,000 allied troops under direct NATO command with each existing battle groups sharply strengthened — Poland's went from 1,010 troops to 10,500 — while four new battle groups were set up in Slovakia, Hungary, Romania and Bulgaria.

Furthermore, many European countries have requested additional US troops on their soil under bilateral agreements, bringing the total number of American soldiers across Europe to about 100,000 — the highest level since 2005.

Russia's aggression has also led European NATO members to pledge to significantly up their defense spending in order to reach the alliance's target of 2% of GDP.

NATO members have also started a "reset" of their strategy, promising to strengthen deployments and capabilities on the ground, at sea and in the air, even further. More details on this strategy is due to be unveiled at a summit in June.

Additionally, two European countries — Sweden and Finland — have now officially requested to join the defense alliance, which would effectively double the length of the alliance's shared border with Russia.