India Converted Half of Asia Without an Army.
One of the largest cultural expansions in history was carried out almost entirely by merchants waiting for the monsoon wind to change.
Over roughly a thousand years India gave much of Asia its religions, its epics, its scripts and its ideas of kingship, using convoys timed to the monsoon's twice-yearly reversal rather than armies. Buddhism set aside caste and the food laws that made travel among strangers difficult, and it moved east in the holds of merchant ships until, by one count, China had thirty thousand monasteries and close to two million monks. The courts of Southeast Asia adopted Sanskrit, Indian law and Indian statecraft by choice, judging it the best system on offer to a king who wanted to look legitimate at home and abroad. The former Thai capital Ayutthaya took its name from Ayodhya, the city of Rama. Angkor Wat, the largest religious monument on earth, is a working diagram of the Indian cosmos, its moat standing for the ocean that surrounds Mount Meru.
The era's other great power took a different route. China's Confucian order required a foreign ruler to acknowledge the emperor as his superior before exchange could happen, tribute, not trade. The ports of the region answered to Chinese demand while its temples, script and kingship were Indian-influenced.
It wasn't wholly peaceful. The Indianised kingdoms fought each other readily enough. What the pattern lacked, for the better part of a thousand years, was an Indian conqueror.
I've written up the full story, with sources and further reading. Link to essay in the comments below.