Most countries to support an ally in war
Who
67 nations
Where
Korea, Republic of (Seoul)
When
The most countries to support an ally in war is 67 and was achieved by nations supporting the Republic of Korea during the Korean War of 1950-1953. This included military and non-military support of the United Nations-backed Republic of Korea. The war began on 25 June 1950 and ended on 27 July 1953.