The major factor that led to growth in Japan during the Tokugawa period was peace. The Tokugawa Shogunate took control of the country and ended the "Warring States" period that had lasted for over 100 years. Starting in 1638, Japan enojoyed over 200 years in which there was no warfare in Japan and in which there was no significant political change.
By doing this, the Tokugawa created stability in the country. The stability and peace that the Tokugawa created allowed the Japanese economy to grow since it was not continually being devastated by war. In addition, trade became much more possible as the country became more unified.
By creating a peaceful and stable country, the Tokugawa laid the foundations for economic growth in Japan.