S- Social
Initially, the spread of Buddhism was started through social interaction between people in South A sea (where the religion originally came from) with the people in East Asia through.
P- Political
The spread of Buddhism also accelerated by the alliances that were formed between some territories in East and South Asia in order to strengthen their military defense.
R- Religious
Some government in East Asia institutionalized Buddhism as their national religion. This exposed Buddhism teaching to all citizens in that territory.
I- Intellectual
Some of popular figure such that were seen as intellectuals often quote the teachings from Buddhism during their lectures and spread the knowledge about the religion.
T- Technology
The invention of technologies such as modern ships allow people to reach other territories in East Asia that never been reached before.
E- Economy
Trades also played roles in the spread of Buddhism. Many traders from South Asia who came into East Asia often brought along monks in their ships. When the monks interacted with the local, they spread Buddhism to East Asia.