Early airplane engines had little power and light weight was very important. Also, early aerofoil sections were very thin, and could not have strong frame installed within. So until the 1930s, most wings were too light weight to have enough strength and external bracing struts and wires were added. When the available engine power increased during the 1920s and 1930s, wings could be made heavy and strong enough that bracing was not needed anymore. This type of unbraced wing is called a cantilever wing.