What convention or meeting launched the Women's Suffrage movement?

Seneca Falls convention.

Explanation:

This convention that was held in July 1848. was the beginning of movement. There they reflected of Declaration of Independence. "Are men are born equal" they said, but in this cases men are not all human being, only males. That cannot be accepted. And it wasn't. Seneca Falls started the movement, which spread across the whole world.