The origin of the alliance can be traced back to the Second World War. The UK and the US decided to share intelligence after successfully breaking German and Japanese codes, respectively.
In 1943, the Britain-USA (BRUSA) Agreement laid the foundations for what would become the UK-USA (UKUSA) agreement. The UKUSA was signed in 1946. Canada joined it in 1949, and New Zealand and Australia did so in 1956, forming the alliance.
In recent years, common interests, such as balancing the rise of China, have led to a closer alignment among the Five Eyes countries. Some have attributed their closeness to a common language and mutual trust built over decades of association.
They exchange views of mutual interest compare best practices, hold conference calls throughout the year and gather in person annually. Meanwhile, the US has also sought to exert its influence through other groupings with like-minded countries on issues of security, like the Quadrilateral Security Dialogue (QUAD) featuring itself, Japan, Australia and India. The AUKUS grouping similarly includes Australia, the UK and the US