In the western front, they used Trench Warfare Method
In Trench Warfare the opposing teams would build some sort of trench surrounding their defended area to prevent the the opposing team in invading their protected Area. It's best used as a Defensive method which require the armies to stay hold and defended their position. That's why they're not moving so much
Answer: Bassically, certain gasses like CO2 (Carbon Dioxide) that come from stuff like burning fossil fuels and global warming, they heat up the earth, are wastes and are used as fuel.
