Why iron and steel industry is called the backbone of moden economy?

Steel and iron are known as the backbone of modern industry because:
1. Almost everything is made of steel or iron, or has been made with tools and machinery off these metal.
2. Ships, trains, trucks and autos are made largely of steel or iron. Even the safety pin are made from steel or iron.
3. Minerals are mined with steel or iron equipments.
4. Large buildings have steel or iron framework.
5. Oil wells are drilled with steel or iron machinery.