the availability of iron and coal
the relative ease of transportation
an energetic scientific a large community
labor force
Some other answers are-
new techniques in iron and steel production
the development of the idea of interchangeable parts
the change from artisan-produced items to machine-produced, or mass-produced, parts
the division of labor and the assembly line
the creation of “factories” or “mill towns” where workers could come to a central location to work