This is key.
They cannot force me to go to war, what are they gonna do, give me a gun? I’ll defend myself with it. Take me to jail? Shelter and food, even better than war.
The only factor “forcing” (convincing) people to go fight in the trenches is social status. They know social pressure is a very powerful tool and the use it. When they need peple fighting for the country they lift up soldiers into a higher status level: Discounts for veterans, discounts for soldiers and their family, wage raises, custom housing and life saving plans, and culture and movies praising the “bravery” inside war. Not to mention the social rejection targeted towards deserters. It’s all rigged to make us crave it.