TL:DR Chemical gas is a war crime due to the amount of suffering it causes. Mustard gas burns the skin, Phosgene is impossible to see, and Chlorine can make you drown in your own body.
Machine guns had been in use and invented since 1908, with invention of weapons such as the Vickers and German Maschinegewehr 08. Trench warfare wasn't a weapon, but more of a tactic. Mines weren't a war crime either as they most likely weren't deemed to cause "unneeded suffering" and their purpose usually was to simply discourage the travel of an area. Usually, if you stepped on a mine you'd die.
Meanwhile, Chemical gas was simply invented on accident as the German Empire's scientist,
Answer: It was bordered by enemies on two fronts. Attack France in the West before Russia in the East had a chance to mobilize. Heavy casualties and little territorial gain.
The founding fathers agreed with the concept of separation of powers and checks and balances in government. The founding fathers agreed that truly enlightened governments made the right decisions for their citizens. This is the answer i think if not then i'm so sorry.
