I assume the answer is mostly geographical, but not having formal relations with one of two neighbors for 50 years without having a war is pretty odd. (politics.stackexchange.com)
It was a symbol of the Centennial Celebration of formal relations between Japan and the United States - the first such affiliation on the West coast. (sandiegoboattours.com)
Some proposals for formal relations between government and a national body to review government performance are put forward in the «Relations with the Commonwealth Government» section later in the Issues Paper. (humanrights.gov.au)