The Group of Seven may be a small, elite club, but when its leaders gather in Canada, several other national heads will attend as guests — highlighting the group's efforts to adapt to a fast-changing world.

The leaders of India, Ukraine, Mexico, South Africa and South Korea are among a carefully selected guest list drawn up at a time of global turmoil and a radical new U.S. approach to world affairs.

Summit invitations have become part of the G7 routine, and the host nation often likes to make a "welcome-to-this-exclusive-club" gesture, said Ananya Kumar, of the Atlantic Council's GeoEconomics Center.