As the title says: could the autogyro have been invented before the fixed-wing aircraft? And how would, for instance, WWI, or the interwar airline industry, have been affected if the former, rather than the latter, were in service?
Unlike helicopters, which require high power-to-weight ratios, the autogyro has similar requirements to the fixed-wing aeroplane. It also has simpler controls than either — both pitch and roll simply involve tilting the rotorhead, which (unlike in a helicopter) isn't trying to transmit power at the same time (which also means you don't have torque necessitating a tailrotor). So I think from an engineering point of view an autogyro could have been built in 1903, had anyone known how...