In WWI trenches helped out the countries a lot because they protected them a lot from machine guns and other military weapons.
Medical advances during WWI where important because there was a deadly disease called Typhoid, they had a lot of vaccinations for diseases. Vehicles started to have mobile X-rays. The soldiers also were trained to be more hygiene.
All the nations agreed to stop fighting and signed the Treaty Of Versailles, as long as all the terms of peace were reached. Germany had to pay for the repairs of what they destroyed during the War of WWI.