How can war affect your mental health?

Many different ways: It's hard to give a short answer, as the impact depends on the experiences a person had during the war- a few examples: whether a person was civilian or a soldier, whether a victim or perpetrator of acts of violence, how those acts were seen at the time, and whether he/she ended up on the winning or losing side. Many, but not all survivors end up suffering from depression and ptsd.

Global mental health: I agree with dr. Raina about the effects of war on individual mental health. However, these effects go far beyond this into the universal. For instance, we cannot know the full effects on developing children whose parents are deployed for long periods, or killed. Also when we harm others, we inflict suffering that magnifies with each person touched. The results extend outward, indefinitely.

New or worse: War can cause a mental health issue to emerge and/or exacerbate one that exist. Those already struggling with or who have struggled with mental health issues are more prone to mental health issues when life stressors develop such as war.