Mechanised warfare was largely introduced during World War 1. Although initially (and for most of the war) the technologies and equipment wasn't necessarily immediately very effective, they were somewhat effective, and most importantly, their concept was well proved. Tanks allowed soldiers to advance and engage enemies from relative safety, most bullets couldn't penetrate the tank, soldiers from inside tanks engaged enemies using machine guns and turrets/howitzers/cannons. The tanks were very slow and cumbersome, many times resulting in inefficiencies. There was no guidance or targeting systems, aiming and striking an enemy was difficult. The tank proved to armies that it was possible to move and engage enemies, with almost complete safety against general infantry unit's equipment ( e.g rifle bullets, grenades, machine guns). This concept was carried through to future wars, most notably WW2, where tanks were vastly improved gaining relative speed and agility, more firepower and accuracy, as well as many other improvements. Air planes used during World War 1 were largely for scouting and reconnaissance, there are accounts of pilots in WW1 manually dropping bombs out the cockpit with their bare hands. The intelligence and birds eye view of the battlefield proved them to be valuable, this was carried through to future wars, and their firepower and ability to strike targets was improved in future wars.
