Russia has launched a military operation in Ukraine – a cross-border offensive closely resembling 2014's illegal annexation of Crimea.
NATO had no forces on its eastern flank eight years ago and described the events in Crimea as a "wake-up call".
So, what has the military alliance done in countries bordering Russia, Ukraine and the Black Sea between 2014 and the latest invasion?
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Aftermath of 2014
Immediately, NATO boosted its air defence, policing and surveillance capabilities – adding another Baltic air policing base in Estonia to the one in Lithuania.
The Readiness Action Plan (RAP) agreed at NATO's 2014 Wales Summit made assurances to bolster security in Eastern Europe through increased military exercises, alongside new headquarters in central and Eastern Europe as a launchpad for greater force strength.
This reshape included tripling the strength of the NATO Response Force (high readiness and special forces) to 40,000, including a new Very High Readiness Joint Task Force of 5,000, and developing the alliance's naval forces in areas including the Black Sea.
Warsaw's 2016 Summit saw the RAP implemented and created its Enhanced Forward Presence – four multinational battalion-size battlegroups in Estonia (led by UK troops on Operation Cabrit), Latvia, Lithuania and Poland.
Watch: Where is NATO deployed in Europe? (Accurate as of 26 January).
Build-up to 2022
For months leading up to their offensive, Russia developed a military presence near its border with Ukraine for exercises, citing the perceived threat of NATO membership expansion as justification as it did in the run-up to 2014.
This prompted international condemnation and bolstered security measures from NATO.
In January 2022, the US placed 8,500 US-based military personnel on high readiness for NATO response; Spain, Denmark and the Netherlands were among NATO members sending more aircraft and ships to Eastern Europe and the Baltic Sea.
Soon after, the UK committed to doubling its troop strength in Estonia and sending four extra Typhoon fighter jets to Cyprus and the Mediterranean, with Royal Marines and Royal Engineers sent to Poland on bilateral missions.
February has seen France offer to lead a new battlegroup in Romania, while the US announced plans to send an additional 3,000 troops to Romania, Poland and Germany.