When the US Marines started adventuring around in Central America after the introduction of the Thompson, they discovered that much better results could be achieved with the dividing of the squad into three four-man fireteams. However, the military was conservative and forced them back to squad tactics. Communist China developed a three-man fireteam concept during their war with the KMT, and later spread it throughout SE Asia.
Camouflage was experimented with during WWI by the Germans, who further developed it during WWII.
What if these ideas became more prevalent during the interwar period, leading to several major armies adopting them and thoroughly implementing them during WWII?