In 1986, Yamada was invited by Pope John Paul II to be one of the few non-Christian religious leaders to attend the World Day of Prayer for Peace in Assisi, Italy.

[2] This event has been held annually to the present day, inviting religious leaders to gather to pray for worldwide peace and reconciliation.

[3] Yamada conducted ecumenical dialogues with religious leaders around the world based on his interpretation of the Lotus Sutra which culminated in a 1987 summit.

He also used the Lotus Sutra to move his sect from a "temple Buddhism" perspective to one based on social engagement.

[4][5] Yamada received the Niwano Peace Prize in 1989, to date he is the only Japanese recipient of the award.