No actually the cavalry should be the first one mechanised. Early vehicles were some sort of an wierd things that wouldnt last long. But the armored cars were lightly armored but enough to not be penetrated by infantry to infantry weapons and as they evolved to be more agile and then by the middle of WW2. The cavalry excluded and no the apcs werent created worldwide untill the late 50s the earliesed were in Germany in the late 30s. And the tank could be created as fast allterrain vehicles since the tracks are good on off road.