<span>Peter Minuit , Hope this helps</span>
D, US involvement in the Korean Civil war lead to increase in military spending
Two inventions from the World War two are the radar and the sonar, both of which had a huge impact in the war, but also after it, becoming a widely used devices all over the world.
The radar was an invention that was enabling detection of objects in the air. Initially it is was used for detection of planes, as that's where the biggest threat was coming. This device enabled the soldiers and the civilians to be warned about the oncoming danger, but also to be able to respond adequately to the threat.
The sonar was another invention inspired by the war. It had the same basic purpose as the radar, just that it was used for detecting objects in the water. This was a crucial instrument that gave the submarines big advantage in locating the enemy and destroying it, or if not capable of that, being able to move away and avoid it.
In a feudal system, a vassal, akin to a serf in most contexts, in general worked land on a lord's fiefdom in exchange for some of the produce from the land and some military protection.
