Would someone explain the link between tank size in HOI4 and walls ?
OK. First off, there was the cavalry. It was fast, and early infantry feared it, and often would just run away when it came at them. Then, due to horse-based books and movies such as 'My Friend Flicka' and 'National Velvet' and 'A Day at the Races', people started to love the horses and not be so scared of them. Military people just couldn't have this, so they decided to come up with something even scarier than horses had been. They looked around the farm where all the horses were and saw a big thing holding water on a tower. 'Hmm,' they thought. 'What would happen if we put that on wheels and had guns sticking out of it?' Thus the idea for the tank was born.
Of course, they couldn't have anyone see what they were trying to build, so they built a high wall around the compound to keep prying eyes out. It did it's job really well - no one ever was able to see what they were building inside the compound. After a lot of mistakes, they finally had their first prototype tank ready to roll. The problem was, it was too big to fit through the door they had made in the wall for it to get out, and thusly, they couldn't even run the field tests they needed to. Instead of panicking, they decided to make the same tank, only a lot smaller - so small that they were now smaller than the infantry that they were supposed to scare off.
HOI4's sprites are a tribute to these first tanks that were stymied by a wall, and wound up smaller than people.