It was invented by Benjamin Holt in 1904. He wasn't given a patent until December 17, 1907. He invented it because wheels would sink in the soft muddy soil of California and the wagon would get stuck.
The impact in the in the 1900s was not only in agriculture, but in logging and warfare also. The Allies used the caterpillar tractor to transport supplies and troops on the battlefield in WW1.
