Thus the main winners of WW1 - the French - put their faith in 'better trenches' - and built the Maginot Line. Another winner - the British - having breached the Germans defensive trenches with tanks and infantry (and then exploited the breakthroughs with cavalry and fast armoured cars), put their faith in heavy, slow moving, 'Infantry Tanks' (such as the Matilda) and light, fast, 'Cruiser Tanks' (a cavalry replacement). Although on the 'winning side', the Americans gained nothing from WW1. The American public, horrified at the losses in the trenches, dismantled their military and vowed never to get involved in another European war again. The main losers of WW1 - the Germans - were forced to dismantle their military. Accepting that defensive trenches won't work, they developed a way to win without trenches - and in a way that would counter the (British) 'Infantry Tank' approach. This was 'Blitzkrieg' - an attack with a fast moving and fast reacting concentrated mass of speedy 'medium' tanks along with aircraft that would act as the supporting artillery (i.e. the Stuka dive-bomber) since real artillery was much too slow moving to keep up. The other loser of WW1 was the Russians. Whilst they retained a massive army, like the Germans they fell into dictatorship. Unfortunately (for the Red Army) Stalin saw the military as a threat to be 'purged', unlike Hitler who saw them as a force to be built up and used "in the pursuit of politics by other means".
In a time of peace, the slower a new design was introduced the better. It allowed any new weapon to be properly developed and tested and then improved over years before being introduced gradually to keep the costs of scrapping the old equipment down. Technology was changing so fast in the air that specifications were often out of date even before being issued. Aircraft were essentially hand-built, with no production line and no standardisation, often fewer than a dozen would be delivered before the replacement arrived. In any event all the focus was on building bombers - with which the RAF believed they would win the war. Any really revolutionary designs or technology has to be suppressed. True innovation - such as the jet engine - would make large amounts of existing equipment obsolete - leading to huge costs (something the committees were set up to prevent). Even significant improvements (such as the monoplane and, later, all metal airframes) would likely be prohibitively expensive. Thus, for example, when it became obvious (in the 1930's) that the standard British anti-tank gun, the 40mm '2 pdr' would be useless in any war against any likely 'enemy' (i.e. the French, with their Char B) it took 2 years to design the replacement (6pdr). This was 'not a problem' during peace time. In fact, the gun design was completed in 1938, 'just in time', although production was not started then because some pen-pusher worked out that one 6pdr would "cost 5 or 6 times that of the 2pdr". So the BEF went to Europe with anti-tank guns that was not very effective against German tanks. Of course after Dunkirk, cost was no longer the issue, but it then turned out that the 'requirements committee' had forgotten the need to design a gun carriage to mount it on - the gun design had been given to the Navy who had no grasp of 'Army matters'. Whilst all the almost useless 2pdrs had been left behind in France, it was calculated that the manufacturers could make 2pdrs 4 times faster than 6pds. So the 2dpr line was cranked up and out they came. When, in the 1930's, it became obvious to some "committees" that war was inevitable many panicked. Whilst some 'got it right' (with, for example, the decision to build the all-metal (high cost) Spitfire) others were only half right (see the Crusader / Covenanter 'cruiser' tank fiasco below).
After the end of the 14-18 war, the Germans were hard pressed to find even the minimum number of officers (as were the Russians), so were forced to promote and train younger (and more flexible) minds. What's more, the Germans had a real equipment shortage.
Indeed, in 1939 they were forced to field even the Panzer 1 (a training tank, armed only with machine guns) and the Panzer II (a 'scout' tank, armed only with a 20mm cannon) to 'make up the numbers'. Their 'main battle tank' was the Panzer III ... and it wasn't only the British that suffered from 'killer committees' (i.e. committees whose decisions that killed people). The Panzer III was designed with a 50mm gun. However, the initial (short barrel) 50mm gun design was not much better than the 37mm PaK36 anti-tank gun with which the Infantry were already equipped. So "in the interest of standardization", the Panzer III was fitted with the same (37mm) gun (but, of course, had a turret designed to mount the larger 50mm gun). Why, you might ask, why didn't they end up 'standardising' by equipping the Infantry with an effective 50mm anti-tank gun ? Well, they 'almost did' ! The 'short barrel' 50mm gun (the Pak37) was designed and ready in 1935. However when it was found to be no better than the 37mm gun, no-one wanted to admit anything. So it took longer than normal for the error (a short barrel) to be corrected. By the time the longer L/60 barrel version (Pak 38) was ready to enter mass production it was 1939 !! The Panzer IV, the German (infantry) Support Tank, was fitted with a 75mm short barrel L/24 gun and available only in small numbers. It's role was intended to be Infantry support - the 75mm gun allowing a decent sized high explosive round for use against pillboxes and fortifications. After encountering the French tanks it was 'almost' up-gunned to the same 50L60 as the Panzer III, however on encountering the T34 it got the somewhat longer 75L43 instead (in March 1942))