Finland and Sweden already have highly capable militaries
Finland has said it wants to join Nato and neighbouring Sweden is expected to make a decision soon.
The move is supported by existing Nato countries, who are supplying Ukraine with weapons to fight Russia’s invasion.
What is Nato?
Nato – the North Atlantic Treaty Organization – is a military alliance. It was formed in 1949 by 12 countries, including the US, UK, Canada and France.
Members agree to come to one another’s aid if they come under armed attack. Finland will take it to 31 members.
Nato’s original aim was to counter Russian expansion in Europe after World War Two.
How could Finland and Sweden join Nato?
Both countries have been neutral for many years, but public support for joining Nato has grown since Russia invaded Ukraine.
In order to join Nato, countries must be democracies, treat minorities fairly and commit to resolving conflicts peacefully.
They must also provide military support to the alliance.
Both Finland – which has a 1,340km (830 mile) border with Russia – and Sweden have highly capable militaries.
Nato members agree to spend 2% of their GDP on defence. Finland meets this target and Sweden will do so “as soon as possible”.