A large portion of defense spending goes to projects that are overzealous in complexity and scope that end up being canceled several years in due to time and budget constraints. With projects like the Future Combat Systems that would digitally connected every troop, weapon and armament on the battlefield to each other so they could communicate at a higher level and allow for more exact control of battlefield conditions. However this $190 Billion project was canceled several years into the project after billions had been spent, but had there been better cost-benefit analysis to see if the project would still be worth keeping even if the Department of Defense had to cut its budget at the time it was started then there's a good chance that this project would have never taken off in the first place and the taxpayers wouldn't be short nearly $20 Billion. Measures such as preventive cost analysis of a project that look into the likely-tude of projects running over budget and advising against a project if it is unrealistic in its scope are great ways to reduce unnecessary wastes that cause our defense budget to be the largest in the World.
For the history of warfare people have worked to have pointier sticks than their enemies, and it is this that has spurred the of development of weaponry. The greatest example of this being the gatling gun, which was created with the hope that it would make wars too gruesome for men to fight. However that was not the case and it laid the foundation for the machine gun, which has made warfare all too efficient for all men to carry out. If we stopped trying to make better weapons it would eliminate the issue of us killing each other faster every time we have a war which would leave more room for diplomacy to determine the outcome of war.