New Zealand pressed for EAS membership, with Australia, and once it was accepted into the club, it pressed for the United States to join.
Mr Key will use the EAS summit to meet Japanese Prime Minister Shinzo Abe today for the first time.
Essentially, the East Asia Summit is a vehicle for the 10 Asean countries to express their collective clout. And the membership of the group shows just what clout it has.
It's Asean plus eight: United States, China, Russia, India, Japan, Korea, Australia and New Zealand.
Asean has a rotating chairmanship. This year it's Brunei; next year, Burma.
Its biggest step was launching in Cambodia last year a set of free trade talks known as the Regional Comprehensive Economic Partnership, RCEP.
The RCEP includes China but not the US, which is effectively leading the Trans Pacific Partnership talks.
Alphabet soup
* All 12 countries involved in the TPP trade talks belong to Apec but not all 21 Apec nations are in the talks.
* All 16 countries involved in the RCEP trade talks belong to the East Asia Summit but two members of the EAS, Russia and the US, are not involved in the RCEP.
* Seven countries are involved in both the TPP and RCEP, including New Zealand.
* All 10 members of Asean are in the 18-strong East Asia Summit.
* Three members of Asean are not members of Apec: Burma, Cambodia, Laos.
* Only one country in the East Asia Summit, India, is not part of Apec or Asean.