Which industry is often referred to as the backbone of the modern industry and why?

Iron and steel industry is often referred to as the backbone of the modern industry because almost everything is either made from iron or steel or has been made using tools and
machineries of these metals. There are plenty of examples like -ships, trains, vehicles; all are made largely of steel. Materials of our day-to-day use starting safety pin to our building in which we live, are made from steel. Without the use of iron no industry can run.