Generally, war did stop in the winter mainly due to the problems involving health and logistics. During the Revolutionary and Napoleonic Wars, troops were sent to barracks or quartered in villages to rest and train as marching would have been difficult due to the problems with weather.
Basically the climate is so cold, there can be lack of resources like food especially, habitats of animals can be destroyed, houses of destroyed no place to live for people, it would be really hard to live outside in freezing cold.
