The rubber tree grows in South America, and originally rubber was found only in South America.
When Europeans first saw rubber in South America, they were astonished. The sight of children playing with the liquid from the rubber trees, rolling it into a ball and bouncing it around, was quite a wonder to them.
The Europeans immediately took the rubber back to their own countries. They had no idea what to do with them, and at first they used them to make erasers, but they could not find a good use for them because fresh rubber is very hard to handle and sticks to the surface after a long time.
Then one day, an American named Goodyear made a great discovery. He found that when raw rubber was heated with sulfur, it held together well and did not become sticky.
Since then, the popularity of rubber has skyrocketed, and it has been used in a variety of products such as rubber bands and automobile tires at an incredible rate.
By the way, the question is why rubber expands and contracts. It is thought that this is because the tiny grains that make up rubber are themselves connected like a long wedge. When this wedge is pulled, the individual rings stretch out, and when it is released, it returns to its original shape, thus allowing the rubber to stretch and shrink freely.

Today, with the development of the chemical industry, synthetic rubbers are made from petroleum, which have various properties that natural rubber does not have.